Auto merge of #12178 - frewsxcv:prefs, r=emilio

Refactor `util::prefs` operations to be methods on static struct.

<!-- Please describe your changes on the following line: -->

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [ ] These changes fix #__ (github issue number if applicable).

<!-- Either: -->
- [ ] There are tests for these changes OR
- [X] These changes do not require tests because _____

<!-- Pull requests that do not address these steps are welcome, but they will require additional verification as part of the review process. -->

<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="35" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/12178)
<!-- Reviewable:end -->

30 files changed, 166 insertions, 162 deletions

diff --git a/components/compositing/compositor.rs b/components/compositing/compositor.rs
index 92283558b9d..b77847eb1c8 100644
--- a/components/compositing/compositor.rs
+++ b/components/compositing/compositor.rs
@@ -49,8 +49,9 @@ use time::{precise_time_ns, precise_time_s};
 use touch::{TouchHandler, TouchAction};
 use url::Url;
 use util::geometry::{PagePx, ScreenPx, ViewportPx};
+use util::opts;
+use util::prefs::PREFS;
 use util::print_tree::PrintTree;
-use util::{opts, prefs};
 use webrender;
 use webrender_traits::{self, ScrollEventPhase};
 use windowing::{self, MouseWindowEvent, WindowEvent, WindowMethods, WindowNavigateMsg};
@@ -1871,7 +1872,7 @@ impl<Window: WindowMethods> IOCompositor<Window> {
 
     fn on_touchpad_pressure_event(&self, cursor: TypedPoint2D<DevicePixel, f32>, pressure: f32,
                                   phase: TouchpadPressurePhase) {
-        if let Some(true) = prefs::get_pref("dom.forcetouch.enabled").as_boolean() {
+        if let Some(true) = PREFS.get("dom.forcetouch.enabled").as_boolean() {
             match self.find_topmost_layer_at_point(cursor / self.scene.scale) {
                 Some(result) => result.layer.send_touchpad_pressure_event(self, result.point, pressure, phase),
                 None => {},
diff --git a/components/constellation/constellation.rs b/components/constellation/constellation.rs
index 1439f24b0b2..585fc5372fe 100644
--- a/components/constellation/constellation.rs
+++ b/components/constellation/constellation.rs
@@ -60,7 +60,7 @@ use timer_scheduler::TimerScheduler;
 use url::Url;
 use util::geometry::PagePx;
 use util::opts;
-use util::prefs::mozbrowser_enabled;
+use util::prefs::PREFS;
 use util::thread::spawn_named;
 use webrender_traits;
 
@@ -1146,7 +1146,7 @@ impl<Message, LTF, STF> Constellation<Message, LTF, STF>
     }
 
     fn handle_alert(&mut self, pipeline_id: PipelineId, message: String, sender: IpcSender<bool>) {
-        let display_alert_dialog = if mozbrowser_enabled() {
+        let display_alert_dialog = if PREFS.is_mozbrowser_enabled() {
             let parent_pipeline_info = self.pipelines.get(&pipeline_id).and_then(|source| source.parent_info);
             if let Some(_) = parent_pipeline_info {
                 let root_pipeline_id = self.root_frame_id
@@ -1457,7 +1457,7 @@ impl<Message, LTF, STF> Constellation<Message, LTF, STF>
                                    containing_pipeline_id: PipelineId,
                                    subpage_id: SubpageId,
                                    event: MozBrowserEvent) {
-        assert!(mozbrowser_enabled());
+        assert!(PREFS.is_mozbrowser_enabled());
 
         // Find the script channel for the given parent pipeline,
         // and pass the event to that script thread.
@@ -2046,7 +2046,7 @@ impl<Message, LTF, STF> Constellation<Message, LTF, STF>
             if let Some(pipeline_id) = rng.choose(&*pipeline_ids) {
                 if let Some(pipeline) = self.pipelines.get(pipeline_id) {
                     // Don't kill the mozbrowser pipeline
-                    if mozbrowser_enabled() && pipeline.parent_info.is_none() {
+                    if PREFS.is_mozbrowser_enabled() && pipeline.parent_info.is_none() {
                         info!("Not closing mozbrowser pipeline {}.", pipeline_id);
                     } else {
                         // Note that we deliberately do not do any of the tidying up
@@ -2132,7 +2132,7 @@ impl<Message, LTF, STF> Constellation<Message, LTF, STF>
     // https://developer.mozilla.org/en-US/docs/Web/Events/mozbrowserlocationchange
     // Note that this is a no-op if the pipeline is not a mozbrowser iframe
     fn trigger_mozbrowserlocationchange(&self, pipeline_id: PipelineId) {
-        if !mozbrowser_enabled() { return; }
+        if !PREFS.is_mozbrowser_enabled() { return; }
 
         let event_info = self.pipelines.get(&pipeline_id).and_then(|pipeline| {
             pipeline.parent_info.map(|(containing_pipeline_id, subpage_id, frame_type)| {
@@ -2158,7 +2158,7 @@ impl<Message, LTF, STF> Constellation<Message, LTF, STF>
     // https://developer.mozilla.org/en-US/docs/Web/Events/mozbrowsererror
     // Note that this does not require the pipeline to be an immediate child of the root
     fn trigger_mozbrowsererror(&self, pipeline_id: PipelineId, reason: String, backtrace: String) {
-        if !mozbrowser_enabled() { return; }
+        if !PREFS.is_mozbrowser_enabled() { return; }
 
         let ancestor_info = self.get_mozbrowser_ancestor_info(pipeline_id);
 
diff --git a/components/constellation/pipeline.rs b/components/constellation/pipeline.rs
index c2193088557..b86cc7ad695 100644
--- a/components/constellation/pipeline.rs
+++ b/components/constellation/pipeline.rs
@@ -36,7 +36,7 @@ use util;
 use util::geometry::{PagePx, ViewportPx};
 use util::ipc::OptionalIpcSender;
 use util::opts::{self, Opts};
-use util::prefs::{self, Pref};
+use util::prefs::{PREFS, Pref};
 use webrender_traits;
 
 pub enum ChildProcess {
@@ -234,7 +234,7 @@ impl Pipeline {
                 panic_chan: state.panic_chan,
                 script_port: script_port,
                 opts: (*opts::get()).clone(),
-                prefs: prefs::get_cloned(),
+                prefs: PREFS.cloned(),
                 layout_to_paint_chan: layout_to_paint_chan,
                 pipeline_port: pipeline_port,
                 pipeline_namespace_id: state.pipeline_namespace_id,
@@ -378,7 +378,7 @@ impl Pipeline {
     pub fn trigger_mozbrowser_event(&self,
                                      subpage_id: SubpageId,
                                      event: MozBrowserEvent) {
-        assert!(prefs::mozbrowser_enabled());
+        assert!(PREFS.is_mozbrowser_enabled());
 
         let event = ConstellationControlMsg::MozBrowserEvent(self.id,
                                                              subpage_id,
diff --git a/components/gfx/font_cache_thread.rs b/components/gfx/font_cache_thread.rs
index b0a156c4a17..9a88cce953b 100644
--- a/components/gfx/font_cache_thread.rs
+++ b/components/gfx/font_cache_thread.rs
@@ -24,7 +24,7 @@ use string_cache::Atom;
 use style::font_face::{EffectiveSources, Source};
 use style::properties::longhands::font_family::computed_value::FontFamily;
 use url::Url;
-use util::prefs;
+use util::prefs::PREFS;
 use util::thread::spawn_named;
 use webrender_traits;
 
@@ -456,7 +456,7 @@ impl FontCacheThread {
 
 // derived from http://stackoverflow.com/a/10864297/3830
 fn is_supported_font_type(toplevel: &TopLevel, sublevel: &SubLevel) -> bool {
-    if !prefs::get_pref("network.mime.sniff").as_boolean().unwrap_or(false) {
+    if !PREFS.get("network.mime.sniff").as_boolean().unwrap_or(false) {
         return true;
     }
 
diff --git a/components/net/http_loader.rs b/components/net/http_loader.rs
index 593ae3e1ead..108cc9b4da1 100644
--- a/components/net/http_loader.rs
+++ b/components/net/http_loader.rs
@@ -51,7 +51,7 @@ use time::Tm;
 #[cfg(any(target_os = "macos", target_os = "linux"))]
 use tinyfiledialogs;
 use url::{Url, Position};
-use util::prefs;
+use util::prefs::PREFS;
 use util::thread::spawn_named;
 use uuid;
 
@@ -860,7 +860,7 @@ pub fn load<A, B>(load_data: &LoadData,
                   user_agent: String,
                   cancel_listener: &CancellationListener)
                   -> Result<StreamedResponse, LoadError> where A: HttpRequest + 'static, B: UIProvider {
-    let max_redirects = prefs::get_pref("network.http.redirection-limit").as_i64().unwrap() as u32;
+    let max_redirects = PREFS.get("network.http.redirection-limit").as_i64().unwrap() as u32;
     let mut iters = 0;
     // URL of the document being loaded, as seen by all the higher-level code.
     let mut doc_url = load_data.url.clone();
diff --git a/components/net/resource_thread.rs b/components/net/resource_thread.rs
index 4cb046566af..f25840de776 100644
--- a/components/net/resource_thread.rs
+++ b/components/net/resource_thread.rs
@@ -48,7 +48,7 @@ use std::sync::{Arc, RwLock};
 use storage_thread::StorageThreadFactory;
 use url::Url;
 use util::opts;
-use util::prefs;
+use util::prefs::PREFS;
 use util::thread::spawn_named;
 use websocket_loader;
 
@@ -106,7 +106,7 @@ pub fn start_sending_sniffed_opt(start_chan: LoadConsumer, mut metadata: Metadat
                                  classifier: Arc<MIMEClassifier>, partial_body: &[u8],
                                  context: LoadContext)
                                  -> Result<ProgressSender, ()> {
-    if prefs::get_pref("network.mime.sniff").as_boolean().unwrap_or(false) {
+    if PREFS.get("network.mime.sniff").as_boolean().unwrap_or(false) {
         // TODO: should be calculated in the resource loader, from pull requeset #4094
         let mut no_sniff = NoSniffFlag::OFF;
         let mut check_for_apache_bug = ApacheBugFlag::OFF;
diff --git a/components/script/dom/bindings/codegen/CodegenRust.py b/components/script/dom/bindings/codegen/CodegenRust.py
index 76aab6b9b53..ac53221cb8a 100644
--- a/components/script/dom/bindings/codegen/CodegenRust.py
+++ b/components/script/dom/bindings/codegen/CodegenRust.py
@@ -2250,7 +2250,7 @@ class CGConstructorEnabled(CGAbstractMethod):
         pref = iface.getExtendedAttribute("Pref")
         if pref:
             assert isinstance(pref, list) and len(pref) == 1
-            conditions.append('prefs::get_pref("%s").as_boolean().unwrap_or(false)' % pref[0])
+            conditions.append('PREFS.get("%s").as_boolean().unwrap_or(false)' % pref[0])
         func = iface.getExtendedAttribute("Func")
         if func:
             assert isinstance(func, list) and len(func) == 1
@@ -5605,7 +5605,7 @@ class CGBindingRoot(CGThing):
             'dom::browsingcontext::BrowsingContext',
             'mem::heap_size_of_raw_self_and_children',
             'libc',
-            'util::prefs',
+            'util::prefs::PREFS',
             'script_runtime::{store_panic_result, maybe_take_panic_result}',
             'std::borrow::ToOwned',
             'std::cmp',
diff --git a/components/script/dom/bindings/guard.rs b/components/script/dom/bindings/guard.rs
index 40faebbd4f2..114045a62e8 100644
--- a/components/script/dom/bindings/guard.rs
+++ b/components/script/dom/bindings/guard.rs
@@ -5,7 +5,7 @@
 //! Machinery to conditionally expose things.
 
 use js::jsapi::{HandleObject, JSContext};
-use util::prefs::get_pref;
+use util::prefs::PREFS;
 
 /// A container with a condition.
 pub struct Guard<T: Clone + Copy> {
@@ -47,7 +47,7 @@ pub enum Condition {
 impl Condition {
     unsafe fn is_satisfied(&self, cx: *mut JSContext, obj: HandleObject) -> bool {
         match *self {
-            Condition::Pref(name) => get_pref(name).as_boolean().unwrap_or(false),
+            Condition::Pref(name) => PREFS.get(name).as_boolean().unwrap_or(false),
             Condition::Func(f) => f(cx, obj),
             Condition::Satisfied => true,
         }
diff --git a/components/script/dom/document.rs b/components/script/dom/document.rs
index 23c50075068..4b4805695da 100644
--- a/components/script/dom/document.rs
+++ b/components/script/dom/document.rs
@@ -127,7 +127,7 @@ use style::servo::Stylesheet;
 use time;
 use url::Url;
 use url::percent_encoding::percent_decode;
-use util::prefs::mozbrowser_enabled;
+use util::prefs::PREFS;
 use util::str::{split_html_space_chars, str_join};
 
 #[derive(JSTraceable, PartialEq, HeapSizeOf)]
@@ -1262,7 +1262,7 @@ impl Document {
     }
 
     pub fn trigger_mozbrowser_event(&self, event: MozBrowserEvent) {
-        if mozbrowser_enabled() {
+        if PREFS.is_mozbrowser_enabled() {
             if let Some((containing_pipeline_id, subpage_id, _)) = self.window.parent_info() {
                 let event = ConstellationMsg::MozBrowserEvent(containing_pipeline_id,
                                                               subpage_id,
diff --git a/components/script/dom/htmlanchorelement.rs b/components/script/dom/htmlanchorelement.rs
index 161a7d43eaf..713aa0a92cb 100644
--- a/components/script/dom/htmlanchorelement.rs
+++ b/components/script/dom/htmlanchorelement.rs
@@ -29,7 +29,7 @@ use std::default::Default;
 use string_cache::Atom;
 use style::attr::AttrValue;
 use url::Url;
-use util::prefs::mozbrowser_enabled;
+use util::prefs::PREFS;
 
 #[dom_struct]
 pub struct HTMLAnchorElement {
@@ -575,7 +575,7 @@ fn follow_hyperlink(subject: &Element, hyperlink_suffix: Option<String>) {
 
     // Step 8: navigate to the URL.
     if let Some(target) = target {
-        if mozbrowser_enabled() && !is_current_browsing_context(target.Value()) {
+        if PREFS.is_mozbrowser_enabled() && !is_current_browsing_context(target.Value()) {
             // https://developer.mozilla.org/en-US/docs/Web/Events/mozbrowseropenwindow
             // TODO: referrer and opener
             // TODO: should we send the normalized url or the non-normalized href?
diff --git a/components/script/dom/htmliframeelement.rs b/components/script/dom/htmliframeelement.rs
index 2c71488c5dc..f1f3c0e29de 100644
--- a/components/script/dom/htmliframeelement.rs
+++ b/components/script/dom/htmliframeelement.rs
@@ -48,7 +48,7 @@ use string_cache::Atom;
 use style::attr::{AttrValue, LengthOrPercentageOrAuto};
 use style::context::ReflowGoal;
 use url::Url;
-use util::prefs::mozbrowser_enabled;
+use util::prefs::PREFS;
 use util::servo_version;
 
 bitflags! {
@@ -145,7 +145,7 @@ impl HTMLIFrameElement {
               .send(ConstellationMsg::ScriptLoadedURLInIFrame(load_info))
               .unwrap();
 
-        if mozbrowser_enabled() {
+        if PREFS.is_mozbrowser_enabled() {
             // https://developer.mozilla.org/en-US/docs/Web/Events/mozbrowserloadstart
             self.dispatch_mozbrowser_event(MozBrowserEvent::LoadStart);
         }
@@ -164,7 +164,7 @@ impl HTMLIFrameElement {
         // TODO(gw): Support mozbrowser event types that have detail which is not a string.
         // See https://developer.mozilla.org/en-US/docs/Web/API/Using_the_Browser_API
         // for a list of mozbrowser events.
-        assert!(mozbrowser_enabled());
+        assert!(PREFS.is_mozbrowser_enabled());
 
         if self.Mozbrowser() {
             let window = window_from_node(self);
diff --git a/components/script/dom/htmlmetaelement.rs b/components/script/dom/htmlmetaelement.rs
index 160b4a9c68e..3a289b6c1bc 100644
--- a/components/script/dom/htmlmetaelement.rs
+++ b/components/script/dom/htmlmetaelement.rs
@@ -70,7 +70,7 @@ impl HTMLMetaElement {
     }
 
     fn apply_viewport(&self) {
-        if !::util::prefs::get_pref("layout.viewport.enabled").as_boolean().unwrap_or(false) {
+        if !::util::prefs::PREFS.get("layout.viewport.enabled").as_boolean().unwrap_or(false) {
             return;
         }
         let element = self.upcast::<Element>();
diff --git a/components/script/dom/mouseevent.rs b/components/script/dom/mouseevent.rs
index d6b5316f2d2..78b1a33005f 100644
--- a/components/script/dom/mouseevent.rs
+++ b/components/script/dom/mouseevent.rs
@@ -17,7 +17,7 @@ use dom::uievent::UIEvent;
 use dom::window::Window;
 use std::cell::Cell;
 use std::default::Default;
-use util::prefs;
+use util::prefs::PREFS;
 
 #[dom_struct]
 pub struct MouseEvent {
@@ -157,7 +157,7 @@ impl MouseEventMethods for MouseEvent {
     // This returns the same result as current gecko.
     // https://developer.mozilla.org/en-US/docs/Web/API/MouseEvent/which
     fn Which(&self) -> i32 {
-        if prefs::get_pref("dom.mouseevent.which.enabled").as_boolean().unwrap_or(false) {
+        if PREFS.get("dom.mouseevent.which.enabled").as_boolean().unwrap_or(false) {
             (self.button.get() + 1) as i32
         } else {
             0
diff --git a/components/script/dom/serviceworkerglobalscope.rs b/components/script/dom/serviceworkerglobalscope.rs
index 4039be05403..6f395863f2f 100644
--- a/components/script/dom/serviceworkerglobalscope.rs
+++ b/components/script/dom/serviceworkerglobalscope.rs
@@ -37,7 +37,7 @@ use std::sync::mpsc::{Receiver, RecvError, Select, Sender, channel};
 use std::sync::{Arc, Mutex};
 use std::time::Instant;
 use url::Url;
-use util::prefs;
+use util::prefs::PREFS;
 use util::thread::spawn_named;
 use util::thread_state;
 use util::thread_state::{IN_WORKER, SCRIPT};
@@ -225,7 +225,7 @@ impl ServiceWorkerGlobalScope {
             scope.mem_profiler_chan().run_with_memory_reporting(|| {
                 // Service workers are time limited
                 let sw_lifetime = Instant::now();
-                let sw_lifetime_timeout = prefs::get_pref("dom.serviceworker.timeout_seconds").as_u64().unwrap();
+                let sw_lifetime_timeout = PREFS.get("dom.serviceworker.timeout_seconds").as_u64().unwrap();
                 while let Ok(event) = global.receive_event() {
                     if scope.is_closing() {
                         break;
diff --git a/components/script/dom/testbinding.rs b/components/script/dom/testbinding.rs
index 8cd53ee57fb..ffe8afc0b89 100644
--- a/components/script/dom/testbinding.rs
+++ b/components/script/dom/testbinding.rs
@@ -29,7 +29,7 @@ use js::jsval::{JSVal, NullValue};
 use std::borrow::ToOwned;
 use std::ptr;
 use std::rc::Rc;
-use util::prefs::get_pref;
+use util::prefs::PREFS;
 
 #[dom_struct]
 pub struct TestBinding {
@@ -558,10 +558,10 @@ impl TestBindingMethods for TestBinding {
     fn PassVariadicAny(&self, _: *mut JSContext, _: Vec<HandleValue>) {}
     fn PassVariadicObject(&self, _: *mut JSContext, _: Vec<*mut JSObject>) {}
     fn BooleanMozPreference(&self, pref_name: DOMString) -> bool {
-        get_pref(pref_name.as_ref()).as_boolean().unwrap_or(false)
+        PREFS.get(pref_name.as_ref()).as_boolean().unwrap_or(false)
     }
     fn StringMozPreference(&self, pref_name: DOMString) -> DOMString {
-        get_pref(pref_name.as_ref()).as_string().map(|s| DOMString::from(s)).unwrap_or_else(|| DOMString::new())
+        PREFS.get(pref_name.as_ref()).as_string().map(|s| DOMString::from(s)).unwrap_or_else(|| DOMString::new())
     }
     fn PrefControlledAttributeDisabled(&self) -> bool { false }
     fn PrefControlledAttributeEnabled(&self) -> bool { false }
diff --git a/components/script/dom/window.rs b/components/script/dom/window.rs
index b58fc901316..6f012e9c31e 100644
--- a/components/script/dom/window.rs
+++ b/components/script/dom/window.rs
@@ -96,7 +96,7 @@ use timers::{IsInterval, OneshotTimerCallback, OneshotTimerHandle, OneshotTimers
 use tinyfiledialogs::{self, MessageBoxIcon};
 use url::Url;
 use util::geometry::{self, MAX_RECT};
-use util::prefs::mozbrowser_enabled;
+use util::prefs::PREFS;
 use util::str::HTML_SPACE_CHARACTERS;
 use util::{breakpoint, opts};
 use webdriver_handlers::jsval_to_webdriver;
@@ -1581,7 +1581,7 @@ impl Window {
 
     /// Returns whether this window is mozbrowser.
     pub fn is_mozbrowser(&self) -> bool {
-        mozbrowser_enabled() && self.parent_info().is_none()
+        PREFS.is_mozbrowser_enabled() && self.parent_info().is_none()
     }
 
     /// Returns whether mozbrowser is enabled and `obj` has been created
@@ -1757,4 +1757,3 @@ fn debug_reflow_events(id: PipelineId, goal: &ReflowGoal, query_type: &ReflowQue
 
     println!("{}", debug_msg);
 }
-
diff --git a/components/script/dom/xmlhttprequest.rs b/components/script/dom/xmlhttprequest.rs
index af424fb83d7..7b51e76a37f 100644
--- a/components/script/dom/xmlhttprequest.rs
+++ b/components/script/dom/xmlhttprequest.rs
@@ -62,7 +62,7 @@ use string_cache::Atom;
 use time;
 use timers::{OneshotTimerCallback, OneshotTimerHandle};
 use url::{Url, Position};
-use util::prefs::mozbrowser_enabled;
+use util::prefs::PREFS;
 
 #[derive(JSTraceable, PartialEq, Copy, Clone, HeapSizeOf)]
 enum XMLHttpRequestState {
@@ -581,8 +581,7 @@ impl XMLHttpRequestMethods for XMLHttpRequest {
             // story. See https://github.com/servo/servo/issues/9582
             if let GlobalRoot::Window(win) = self.global() {
                 let is_root_pipeline = win.parent_info().is_none();
-                let is_mozbrowser_enabled = mozbrowser_enabled();
-                is_root_pipeline && is_mozbrowser_enabled
+                is_root_pipeline && PREFS.is_mozbrowser_enabled()
             } else {
                 false
             }
diff --git a/components/script/script_runtime.rs b/components/script/script_runtime.rs
index a2677526e0b..d07491d8ce8 100644
--- a/components/script/script_runtime.rs
+++ b/components/script/script_runtime.rs
@@ -27,7 +27,7 @@ use std::os;
 use std::ptr;
 use time::{Tm, now};
 use util::opts;
-use util::prefs::get_pref;
+use util::prefs::PREFS;
 use util::thread_state;
 
 /// Common messages used to control the event loops in both the script and the worker
@@ -124,30 +124,30 @@ pub unsafe fn new_rt_and_cx() -> Runtime {
 
     // Enable or disable the JITs.
     let rt_opts = &mut *RuntimeOptionsRef(runtime.rt());
-    if let Some(val) = get_pref("js.baseline.enabled").as_boolean() {
+    if let Some(val) = PREFS.get("js.baseline.enabled").as_boolean() {
         rt_opts.set_baseline_(val);
     }
-    if let Some(val) = get_pref("js.ion.enabled").as_boolean() {
+    if let Some(val) = PREFS.get("js.ion.enabled").as_boolean() {
         rt_opts.set_ion_(val);
     }
-    if let Some(val) = get_pref("js.asmjs.enabled").as_boolean() {
+    if let Some(val) = PREFS.get("js.asmjs.enabled").as_boolean() {
         rt_opts.set_asmJS_(val);
     }
-    if let Some(val) = get_pref("js.strict.enabled").as_boolean() {
+    if let Some(val) = PREFS.get("js.strict.enabled").as_boolean() {
         rt_opts.set_extraWarnings_(val);
     }
     // TODO: handle js.strict.debug.enabled
     // TODO: handle js.throw_on_asmjs_validation_failure (needs new Spidermonkey)
-    if let Some(val) = get_pref("js.native_regexp.enabled").as_boolean() {
+    if let Some(val) = PREFS.get("js.native_regexp.enabled").as_boolean() {
         rt_opts.set_nativeRegExp_(val);
     }
-    if let Some(val) = get_pref("js.parallel_parsing.enabled").as_boolean() {
+    if let Some(val) = PREFS.get("js.parallel_parsing.enabled").as_boolean() {
         JS_SetParallelParsingEnabled(runtime.rt(), val);
     }
-    if let Some(val) = get_pref("js.offthread_compilation_enabled").as_boolean() {
+    if let Some(val) = PREFS.get("js.offthread_compilation_enabled").as_boolean() {
         JS_SetOffthreadIonCompilationEnabled(runtime.rt(), val);
     }
-    if let Some(val) = get_pref("js.baseline.unsafe_eager_compilation.enabled").as_boolean() {
+    if let Some(val) = PREFS.get("js.baseline.unsafe_eager_compilation.enabled").as_boolean() {
         let trigger: i32 = if val {
             0
         } else {
@@ -157,7 +157,7 @@ pub unsafe fn new_rt_and_cx() -> Runtime {
                                       JSJitCompilerOption::JSJITCOMPILER_BASELINE_WARMUP_TRIGGER,
                                       trigger as u32);
     }
-    if let Some(val) = get_pref("js.ion.unsafe_eager_compilation.enabled").as_boolean() {
+    if let Some(val) = PREFS.get("js.ion.unsafe_eager_compilation.enabled").as_boolean() {
         let trigger: i64 = if val {
             0
         } else {
@@ -171,14 +171,14 @@ pub unsafe fn new_rt_and_cx() -> Runtime {
     // TODO: handle js.asyncstack.enabled (needs new Spidermonkey)
     // TODO: handle js.throw_on_debugee_would_run (needs new Spidermonkey)
     // TODO: handle js.dump_stack_on_debugee_would_run (needs new Spidermonkey)
-    if let Some(val) = get_pref("js.werror.enabled").as_boolean() {
+    if let Some(val) = PREFS.get("js.werror.enabled").as_boolean() {
         rt_opts.set_werror_(val);
     }
     // TODO: handle js.shared_memory.enabled
-    if let Some(val) = get_pref("js.mem.high_water_mark").as_i64() {
+    if let Some(val) = PREFS.get("js.mem.high_water_mark").as_i64() {
         JS_SetGCParameter(runtime.rt(), JSGCParamKey::JSGC_MAX_MALLOC_BYTES, val as u32 * 1024 * 1024);
     }
-    if let Some(val) = get_pref("js.mem.max").as_i64() {
+    if let Some(val) = PREFS.get("js.mem.max").as_i64() {
         let max = if val <= 0 || val >= 0x1000 {
             -1
         } else {
@@ -187,8 +187,8 @@ pub unsafe fn new_rt_and_cx() -> Runtime {
         JS_SetGCParameter(runtime.rt(), JSGCParamKey::JSGC_MAX_BYTES, max as u32);
     }
     // NOTE: This is disabled above, so enabling it here will do nothing for now.
-    if let Some(val) = get_pref("js.mem.gc.incremental.enabled").as_boolean() {
-        let compartment = if let Some(val) = get_pref("js.mem.gc.per_compartment.enabled").as_boolean() {
+    if let Some(val) = PREFS.get("js.mem.gc.incremental.enabled").as_boolean() {
+        let compartment = if let Some(val) = PREFS.get("js.mem.gc.per_compartment.enabled").as_boolean() {
             val
         } else {
             false
@@ -202,67 +202,67 @@ pub unsafe fn new_rt_and_cx() -> Runtime {
         };
         JS_SetGCParameter(runtime.rt(), JSGCParamKey::JSGC_MODE, mode as u32);
     }
-    if let Some(val) = get_pref("js.mem.gc.incremental.slice_ms").as_i64() {
+    if let Some(val) = PREFS.get("js.mem.gc.incremental.slice_ms").as_i64() {
         if val >= 0 && val < 100000 {
             JS_SetGCParameter(runtime.rt(), JSGCParamKey::JSGC_SLICE_TIME_BUDGET, val as u32);
         }
     }
-    if let Some(val) = get_pref("js.mem.gc.compacting.enabled").as_boolean() {
+    if let Some(val) = PREFS.get("js.mem.gc.compacting.enabled").as_boolean() {
         JS_SetGCParameter(runtime.rt(), JSGCParamKey::JSGC_COMPACTING_ENABLED, val as u32);
     }
-    if let Some(val) = get_pref("js.mem.gc.high_frequency_time_limit_ms").as_i64() {
+    if let Some(val) = PREFS.get("js.mem.gc.high_frequency_time_limit_ms").as_i64() {
         if val >= 0 && val < 10000 {
             JS_SetGCParameter(runtime.rt(), JSGCParamKey::JSGC_HIGH_FREQUENCY_TIME_LIMIT, val as u32);
         }
     }
-    if let Some(val) = get_pref("js.mem.gc.dynamic_mark_slice.enabled").as_boolean() {
+    if let Some(val) = PREFS.get("js.mem.gc.dynamic_mark_slice.enabled").as_boolean() {
         JS_SetGCParameter(runtime.rt(), JSGCParamKey::JSGC_DYNAMIC_MARK_SLICE, val as u32);
     }
     // TODO: handle js.mem.gc.refresh_frame_slices.enabled
-    if let Some(val) = get_pref("js.mem.gc.dynamic_heap_growth.enabled").as_boolean() {
+    if let Some(val) = PREFS.get("js.mem.gc.dynamic_heap_growth.enabled").as_boolean() {
         JS_SetGCParameter(runtime.rt(), JSGCParamKey::JSGC_DYNAMIC_HEAP_GROWTH, val as u32);
     }
-    if let Some(val) = get_pref("js.mem.gc.low_frequency_heap_growth").as_i64() {
+    if let Some(val) = PREFS.get("js.mem.gc.low_frequency_heap_growth").as_i64() {
         if val >= 0 && val < 10000 {
             JS_SetGCParameter(runtime.rt(), JSGCParamKey::JSGC_LOW_FREQUENCY_HEAP_GROWTH, val as u32);
         }
     }
-    if let Some(val) = get_pref("js.mem.gc.high_frequency_heap_growth_min").as_i64() {
+    if let Some(val) = PREFS.get("js.mem.gc.high_frequency_heap_growth_min").as_i64() {
         if val >= 0 && val < 10000 {
             JS_SetGCParameter(runtime.rt(), JSGCParamKey::JSGC_HIGH_FREQUENCY_HEAP_GROWTH_MIN, val as u32);
         }
     }
-    if let Some(val) = get_pref("js.mem.gc.high_frequency_heap_growth_max").as_i64() {
+    if let Some(val) = PREFS.get("js.mem.gc.high_frequency_heap_growth_max").as_i64() {
         if val >= 0 && val < 10000 {
             JS_SetGCParameter(runtime.rt(), JSGCParamKey::JSGC_HIGH_FREQUENCY_HEAP_GROWTH_MAX, val as u32);
         }
     }
-    if let Some(val) = get_pref("js.mem.gc.high_frequency_low_limit_mb").as_i64() {
+    if let Some(val) = PREFS.get("js.mem.gc.high_frequency_low_limit_mb").as_i64() {
         if val >= 0 && val < 10000 {
             JS_SetGCParameter(runtime.rt(), JSGCParamKey::JSGC_HIGH_FREQUENCY_LOW_LIMIT, val as u32);
         }
     }
-    if let Some(val) = get_pref("js.mem.gc.high_frequency_high_limit_mb").as_i64() {
+    if let Some(val) = PREFS.get("js.mem.gc.high_frequency_high_limit_mb").as_i64() {
         if val >= 0 && val < 10000 {
             JS_SetGCParameter(runtime.rt(), JSGCParamKey::JSGC_HIGH_FREQUENCY_HIGH_LIMIT, val as u32);
         }
     }
-    if let Some(val) = get_pref("js.mem.gc.allocation_threshold_mb").as_i64() {
+    if let Some(val) = PREFS.get("js.mem.gc.allocation_threshold_mb").as_i64() {
         if val >= 0 && val < 10000 {
             JS_SetGCParameter(runtime.rt(), JSGCParamKey::JSGC_ALLOCATION_THRESHOLD, val as u32);
         }
     }
-    if let Some(val) = get_pref("js.mem.gc.decommit_threshold_mb").as_i64() {
+    if let Some(val) = PREFS.get("js.mem.gc.decommit_threshold_mb").as_i64() {
         if val >= 0 && val < 10000 {
             JS_SetGCParameter(runtime.rt(), JSGCParamKey::JSGC_DECOMMIT_THRESHOLD, val as u32);
         }
     }
-    if let Some(val) = get_pref("js.mem.gc.empty_chunk_count_min").as_i64() {
+    if let Some(val) = PREFS.get("js.mem.gc.empty_chunk_count_min").as_i64() {
         if val >= 0 && val < 10000 {
             JS_SetGCParameter(runtime.rt(), JSGCParamKey::JSGC_MIN_EMPTY_CHUNK_COUNT, val as u32);
         }
     }
-    if let Some(val) = get_pref("js.mem.gc.empty_chunk_count_max").as_i64() {
+    if let Some(val) = PREFS.get("js.mem.gc.empty_chunk_count_max").as_i64() {
         if val >= 0 && val < 10000 {
             JS_SetGCParameter(runtime.rt(), JSGCParamKey::JSGC_MAX_EMPTY_CHUNK_COUNT, val as u32);
         }
@@ -403,11 +403,11 @@ unsafe extern fn trace_rust_roots(tr: *mut JSTracer, _data: *mut os::raw::c_void
 unsafe fn set_gc_zeal_options(cx: *mut JSContext) {
     use js::jsapi::{JS_DEFAULT_ZEAL_FREQ, JS_SetGCZeal};
 
-    let level = match get_pref("js.mem.gc.zeal.level").as_i64() {
+    let level = match PREFS.get("js.mem.gc.zeal.level").as_i64() {
         Some(level @ 0...14) => level as u8,
         _ => return,
     };
-    let frequency = match get_pref("js.mem.gc.zeal.frequency").as_i64() {
+    let frequency = match PREFS.get("js.mem.gc.zeal.frequency").as_i64() {
         Some(frequency) if frequency >= 0 => frequency as u32,
         _ => JS_DEFAULT_ZEAL_FREQ,
     };
diff --git a/components/script/timers.rs b/components/script/timers.rs
index 989382e80fe..237c354be9f 100644
--- a/components/script/timers.rs
+++ b/components/script/timers.rs
@@ -22,7 +22,7 @@ use std::cmp::{self, Ord, Ordering};
 use std::collections::HashMap;
 use std::default::Default;
 use std::rc::Rc;
-use util::prefs::get_pref;
+use util::prefs::PREFS;
 
 #[derive(JSTraceable, PartialEq, Eq, Copy, Clone, HeapSizeOf, Hash, PartialOrd, Ord, Debug)]
 pub struct OneshotTimerHandle(i32);
@@ -214,7 +214,7 @@ impl OneshotTimers {
     }
 
     pub fn slow_down(&self) {
-        let duration = get_pref("js.timers.minimum_duration").as_u64().unwrap_or(1000);
+        let duration = PREFS.get("js.timers.minimum_duration").as_u64().unwrap_or(1000);
         self.js_timers.set_min_duration(MsDuration::new(duration));
     }
 
diff --git a/components/servo/lib.rs b/components/servo/lib.rs
index 0a3b6c2a7e4..96296b92f09 100644
--- a/components/servo/lib.rs
+++ b/components/servo/lib.rs
@@ -81,8 +81,9 @@ use profile_traits::time;
 use script_traits::ConstellationMsg;
 use std::rc::Rc;
 use std::sync::mpsc::Sender;
+use util::opts;
+use util::prefs::PREFS;
 use util::resource_files::resources_dir_path;
-use util::{opts, prefs};
 
 pub use gleam::gl;
 
@@ -257,7 +258,7 @@ pub fn run_content_process(token: String) {
 
     let unprivileged_content = unprivileged_content_receiver.recv().unwrap();
     opts::set_defaults(unprivileged_content.opts());
-    prefs::extend_prefs(unprivileged_content.prefs());
+    PREFS.extend(unprivileged_content.prefs());
 
     // Enter the sandbox if necessary.
     if opts::get().sandbox {
diff --git a/components/style/properties/longhand/box.mako.rs b/components/style/properties/longhand/box.mako.rs
index 9ec51e960cd..d9195d00df2 100644
--- a/components/style/properties/longhand/box.mako.rs
+++ b/components/style/properties/longhand/box.mako.rs
@@ -58,7 +58,7 @@
             % for value in values:
                 "${value}" => {
                     % if value in experimental_values:
-                        if !::util::prefs::get_pref("layout.${value}.enabled")
+                        if !::util::prefs::PREFS.get("layout.${value}.enabled")
                             .as_boolean().unwrap_or(false) {
                             return Err(())
                         }
diff --git a/components/style/properties/properties.mako.rs b/components/style/properties/properties.mako.rs
index 1ba7dd932ea..d2d07c79a73 100644
--- a/components/style/properties/properties.mako.rs
+++ b/components/style/properties/properties.mako.rs
@@ -950,7 +950,7 @@ impl PropertyDeclaration {
                             }
                         % endif
                         % if property.experimental:
-                            if !::util::prefs::get_pref("${property.experimental}")
+                            if !::util::prefs::PREFS.get("${property.experimental}")
                                 .as_boolean().unwrap_or(false) {
                                 return PropertyDeclarationParseResult::ExperimentalProperty
                             }
@@ -975,7 +975,7 @@ impl PropertyDeclaration {
                         }
                     % endif
                     % if shorthand.experimental:
-                        if !::util::prefs::get_pref("${shorthand.experimental}")
+                        if !::util::prefs::PREFS.get("${shorthand.experimental}")
                             .as_boolean().unwrap_or(false) {
                             return PropertyDeclarationParseResult::ExperimentalProperty
                         }
diff --git a/components/style/stylesheets.rs b/components/style/stylesheets.rs
index 98864868233..5307f226f4b 100644
--- a/components/style/stylesheets.rs
+++ b/components/style/stylesheets.rs
@@ -499,7 +499,7 @@ impl<'a, 'b, Impl: SelectorImpl> AtRuleParser for NestedRuleParser<'a, 'b, Impl>
                 Ok(AtRuleType::WithBlock(AtRulePrelude::FontFace))
             },
             "viewport" => {
-                if ::util::prefs::get_pref("layout.viewport.enabled").as_boolean().unwrap_or(false) {
+                if ::util::prefs::PREFS.get("layout.viewport.enabled").as_boolean().unwrap_or(false) {
                     Ok(AtRuleType::WithBlock(AtRulePrelude::Viewport))
                 } else {
                     Err(())
diff --git a/components/util/opts.rs b/components/util/opts.rs
index a55d7e556f2..70926438540 100644
--- a/components/util/opts.rs
+++ b/components/util/opts.rs
@@ -9,7 +9,7 @@ use euclid::size::{Size2D, TypedSize2D};
 use geometry::ScreenPx;
 use getopts::Options;
 use num_cpus;
-use prefs::{self, PrefValue};
+use prefs::{self, PrefValue, PREFS};
 use resource_files::set_resources_path;
 use std::cmp;
 use std::default::Default;
@@ -605,7 +605,7 @@ pub fn from_cmdline_args(args: &[String]) -> ArgumentParsingResult {
     }
 
     let cwd = env::current_dir().unwrap();
-    let homepage_pref = prefs::get_pref("shell.homepage");
+    let homepage_pref = PREFS.get("shell.homepage");
     let url_opt = if !opt_match.free.is_empty() {
         Some(&opt_match.free[0][..])
     } else {
@@ -745,10 +745,10 @@ pub fn from_cmdline_args(args: &[String]) -> ArgumentParsingResult {
 
     let do_not_use_native_titlebar =
         opt_match.opt_present("b") ||
-        !prefs::get_pref("shell.native-titlebar.enabled").as_boolean().unwrap();
+        !PREFS.get("shell.native-titlebar.enabled").as_boolean().unwrap();
 
     let use_webrender =
-        (prefs::get_pref("gfx.webrender.enabled").as_boolean().unwrap() || opt_match.opt_present("w")) &&
+        (PREFS.get("gfx.webrender.enabled").as_boolean().unwrap() || opt_match.opt_present("w")) &&
         !opt_match.opt_present("z");
 
     let render_api = match opt_match.opt_str("G") {
@@ -830,9 +830,9 @@ pub fn from_cmdline_args(args: &[String]) -> ArgumentParsingResult {
         let pref_name = split[0];
         let value = split.get(1);
         match value {
-            Some(&"false") => prefs::set_pref(pref_name, PrefValue::Boolean(false)),
-            Some(&"true") | None => prefs::set_pref(pref_name, PrefValue::Boolean(true)),
-            _ => prefs::set_pref(pref_name, PrefValue::String(value.unwrap().to_string()))
+            Some(&"false") => PREFS.set(pref_name, PrefValue::Boolean(false)),
+            Some(&"true") | None => PREFS.set(pref_name, PrefValue::Boolean(true)),
+            _ => PREFS.set(pref_name, PrefValue::String(value.unwrap().to_string()))
         };
     }
 
diff --git a/components/util/prefs.rs b/components/util/prefs.rs
index 55c856fa747..d0d96a93035 100644
--- a/components/util/prefs.rs
+++ b/components/util/prefs.rs
@@ -14,9 +14,9 @@ use std::path::PathBuf;
 use std::sync::{Arc, Mutex};
 
 lazy_static! {
-    static ref PREFS: Arc<Mutex<HashMap<String, Pref>>> = {
-        let prefs = read_prefs().unwrap_or(HashMap::new());
-        Arc::new(Mutex::new(prefs))
+    pub static ref PREFS: Preferences = {
+        let prefs = read_prefs().unwrap_or_else(|_| HashMap::new());
+        Preferences(Arc::new(Mutex::new(prefs)))
     };
 }
 
@@ -167,14 +167,6 @@ pub fn read_prefs_from_file<T>(mut file: T)
     Ok(prefs)
 }
 
-pub fn get_cloned() -> HashMap<String, Pref> {
-    PREFS.lock().unwrap().clone()
-}
-
-pub fn extend_prefs(extension: HashMap<String, Pref>) {
-    PREFS.lock().unwrap().extend(extension);
-}
-
 pub fn add_user_prefs() {
     match opts::get().config_dir {
         Some(ref config_path) => {
@@ -194,7 +186,7 @@ fn init_user_prefs(path: &mut PathBuf) {
     path.push("prefs.json");
     if let Ok(file) = File::open(path) {
         if let Ok(prefs) = read_prefs_from_file(file) {
-            extend_prefs(prefs);
+            PREFS.extend(prefs);
         }
     } else {
     writeln!(&mut stderr(), "Error opening prefs.json from config directory")
@@ -215,44 +207,56 @@ fn read_prefs() -> Result<HashMap<String, Pref>, ()> {
     read_prefs_from_file(file)
 }
 
-pub fn get_pref(name: &str) -> Arc<PrefValue> {
-    PREFS.lock().unwrap().get(name).map_or(Arc::new(PrefValue::Missing), |x| x.value().clone())
-}
+pub struct Preferences(Arc<Mutex<HashMap<String, Pref>>>);
 
-pub fn set_pref(name: &str, value: PrefValue) {
-    let mut prefs = PREFS.lock().unwrap();
-    if let Some(pref) = prefs.get_mut(name) {
-        pref.set(value);
-        return;
+impl Preferences {
+    pub fn get(&self, name: &str) -> Arc<PrefValue> {
+        self.0.lock().unwrap().get(name).map_or(Arc::new(PrefValue::Missing), |x| x.value().clone())
     }
-    prefs.insert(name.to_owned(), Pref::new(value));
-}
 
-pub fn reset_pref(name: &str) -> Arc<PrefValue> {
-    let mut prefs = PREFS.lock().unwrap();
-    let result = match prefs.get_mut(name) {
-        None => return Arc::new(PrefValue::Missing),
-        Some(&mut Pref::NoDefault(_)) => Arc::new(PrefValue::Missing),
-        Some(&mut Pref::WithDefault(ref default, ref mut set_value)) => {
-            *set_value = None;
-            default.clone()
-        },
-    };
-    if *result == PrefValue::Missing {
-        prefs.remove(name);
+    pub fn cloned(&self) -> HashMap<String, Pref> {
+        self.0.lock().unwrap().clone()
     }
-    result
-}
 
-pub fn reset_all_prefs() {
-    let names = {
-        PREFS.lock().unwrap().keys().cloned().collect::<Vec<String>>()
-    };
-    for name in names.iter() {
-        reset_pref(name);
+    pub fn is_mozbrowser_enabled(&self) -> bool {
+        self.get("dom.mozbrowser.enabled").as_boolean().unwrap_or(false)
     }
-}
 
-pub fn mozbrowser_enabled() -> bool {
-    get_pref("dom.mozbrowser.enabled").as_boolean().unwrap_or(false)
+    pub fn set(&self, name: &str, value: PrefValue) {
+        let mut prefs = self.0.lock().unwrap();
+        if let Some(pref) = prefs.get_mut(name) {
+            pref.set(value);
+            return;
+        }
+        prefs.insert(name.to_owned(), Pref::new(value));
+    }
+
+    pub fn reset(&self, name: &str) -> Arc<PrefValue> {
+        let mut prefs = self.0.lock().unwrap();
+        let result = match prefs.get_mut(name) {
+            None => return Arc::new(PrefValue::Missing),
+            Some(&mut Pref::NoDefault(_)) => Arc::new(PrefValue::Missing),
+            Some(&mut Pref::WithDefault(ref default, ref mut set_value)) => {
+                *set_value = None;
+                default.clone()
+            },
+        };
+        if *result == PrefValue::Missing {
+            prefs.remove(name);
+        }
+        result
+    }
+
+    pub fn reset_all(&self) {
+        let names = {
+            self.0.lock().unwrap().keys().cloned().collect::<Vec<String>>()
+        };
+        for name in names.iter() {
+            self.reset(name);
+        }
+    }
+
+    pub fn extend(&self, extension: HashMap<String, Pref>) {
+        self.0.lock().unwrap().extend(extension);
+    }
 }
diff --git a/components/webdriver_server/lib.rs b/components/webdriver_server/lib.rs
index d2cedb10858..7e060d74c6a 100644
--- a/components/webdriver_server/lib.rs
+++ b/components/webdriver_server/lib.rs
@@ -46,7 +46,7 @@ use std::sync::mpsc::Sender;
 use std::thread;
 use std::time::Duration;
 use url::Url;
-use util::prefs::{get_pref, reset_all_prefs, reset_pref, set_pref, PrefValue};
+use util::prefs::{PREFS, PrefValue};
 use util::thread::spawn_named;
 use uuid::Uuid;
 use webdriver::command::WindowSizeParameters;
@@ -813,7 +813,7 @@ impl Handler {
                         parameters: &GetPrefsParameters) -> WebDriverResult<WebDriverResponse> {
         let prefs = parameters.prefs
             .iter()
-            .map(|item| (item.clone(), get_pref(item).to_json()))
+            .map(|item| (item.clone(), PREFS.get(item).to_json()))
             .collect::<BTreeMap<_, _>>();
 
         Ok(WebDriverResponse::Generic(ValueResponse::new(prefs.to_json())))
@@ -822,7 +822,7 @@ impl Handler {
     fn handle_set_prefs(&self,
                         parameters: &SetPrefsParameters) -> WebDriverResult<WebDriverResponse> {
         for &(ref key, ref value) in parameters.prefs.iter() {
-            set_pref(key, value.clone());
+            PREFS.set(key, value.clone());
         }
         Ok(WebDriverResponse::Void)
     }
@@ -830,12 +830,12 @@ impl Handler {
     fn handle_reset_prefs(&self,
                           parameters: &GetPrefsParameters) -> WebDriverResult<WebDriverResponse> {
         let prefs = if parameters.prefs.len() == 0 {
-            reset_all_prefs();
+            PREFS.reset_all();
             BTreeMap::new()
         } else {
             parameters.prefs
                 .iter()
-                .map(|item| (item.clone(), reset_pref(item).to_json()))
+                .map(|item| (item.clone(), PREFS.reset(item).to_json()))
                 .collect::<BTreeMap<_, _>>()
         };
         Ok(WebDriverResponse::Generic(ValueResponse::new(prefs.to_json())))
diff --git a/ports/glutin/window.rs b/ports/glutin/window.rs
index 010c337f01b..22f9664fcb2 100644
--- a/ports/glutin/window.rs
+++ b/ports/glutin/window.rs
@@ -36,7 +36,7 @@ use util::geometry::ScreenPx;
 use util::opts;
 #[cfg(not(target_os = "android"))]
 use util::opts::RenderApi;
-use util::prefs;
+use util::prefs::PREFS;
 use util::resource_files;
 #[cfg(target_os = "windows")] use winapi;
 
@@ -822,7 +822,7 @@ impl WindowMethods for Window {
             }
 
             (NONE, Key::Escape) => {
-                if let Some(true) = prefs::get_pref("shell.builtin-key-shortcuts.enabled").as_boolean() {
+                if let Some(true) = PREFS.get("shell.builtin-key-shortcuts.enabled").as_boolean() {
                     self.event_queue.borrow_mut().push(WindowEvent::Quit);
                 }
             }
@@ -865,7 +865,7 @@ impl WindowMethods for Window {
                 self.scroll_window(-LINE_HEIGHT, 0.0, TouchEventType::Move);
             }
             (CMD_OR_CONTROL, Key::R) => {
-                if let Some(true) = prefs::get_pref("shell.builtin-key-shortcuts.enabled").as_boolean() {
+                if let Some(true) = PREFS.get("shell.builtin-key-shortcuts.enabled").as_boolean() {
                     self.event_queue.borrow_mut().push(WindowEvent::Reload);
                 }
             }
diff --git a/tests/unit/net/http_loader.rs b/tests/unit/net/http_loader.rs
index 705331415df..a6f4bc6ef31 100644
--- a/tests/unit/net/http_loader.rs
+++ b/tests/unit/net/http_loader.rs
@@ -33,7 +33,7 @@ use std::sync::mpsc::Receiver;
 use std::sync::{Arc, mpsc, RwLock};
 use std::thread;
 use url::Url;
-use util::prefs;
+use util::prefs::{self, PREFS};
 
 const DEFAULT_USER_AGENT: &'static str = "Test-agent";
 
@@ -1218,8 +1218,8 @@ fn test_load_errors_when_there_is_too_many_redirects() {
     let ui_provider = TestProvider::new();
 
     let redirect_limit = 13.;
-    prefs::set_pref("network.http.redirection-limit",
-                    prefs::PrefValue::Number(redirect_limit));
+    PREFS.set("network.http.redirection-limit",
+              prefs::PrefValue::Number(redirect_limit));
 
     match load(&load_data, &ui_provider, &http_state, None, &Factory,
                DEFAULT_USER_AGENT.to_owned(), &CancellationListener::new(None)) {
@@ -1231,7 +1231,7 @@ fn test_load_errors_when_there_is_too_many_redirects() {
         _ => panic!("expected max redirects to fail")
     }
 
-    prefs::reset_pref("network.http.redirection-limit");
+    PREFS.reset("network.http.redirection-limit");
 }
 
 #[test]
diff --git a/tests/unit/style/viewport.rs b/tests/unit/style/viewport.rs
index 61168d65ad5..2d110e7de39 100644
--- a/tests/unit/style/viewport.rs
+++ b/tests/unit/style/viewport.rs
@@ -30,8 +30,8 @@ fn test_viewport_rule<F>(css: &str,
                          callback: F)
     where F: Fn(&Vec<ViewportDescriptorDeclaration>, &str)
 {
-    ::util::prefs::set_pref("layout.viewport.enabled",
-                            ::util::prefs::PrefValue::Boolean(true));
+    ::util::prefs::PREFS.set("layout.viewport.enabled",
+                             ::util::prefs::PrefValue::Boolean(true));
     let stylesheet = stylesheet!(css, Author, Box::new(CSSErrorReporterTest));
     let mut rule_count = 0;
     for rule in stylesheet.effective_rules(&device).viewport() {
@@ -245,8 +245,8 @@ fn cascading_within_viewport_rule() {
 
 #[test]
 fn multiple_stylesheets_cascading() {
-    ::util::prefs::set_pref("layout.viewport.enabled",
-                            ::util::prefs::PrefValue::Boolean(true));
+    ::util::prefs::PREFS.set("layout.viewport.enabled",
+                             ::util::prefs::PrefValue::Boolean(true));
     let device = Device::new(MediaType::Screen, Size2D::typed(800., 600.));
     let error_reporter = CSSErrorReporterTest;
     let stylesheets = vec![
diff --git a/tests/unit/util/prefs.rs b/tests/unit/util/prefs.rs
index 7deefd398be..295a3e1fe2c 100644
--- a/tests/unit/util/prefs.rs
+++ b/tests/unit/util/prefs.rs
@@ -5,7 +5,7 @@
 use std::fs::{self, File};
 use std::io::{Read, Write};
 use util::basedir;
-use util::prefs::{PrefValue, extend_prefs, read_prefs_from_file, get_pref, set_pref, reset_pref};
+use util::prefs::{PREFS, PrefValue, read_prefs_from_file};
 
 #[test]
 fn test_create_pref() {
@@ -30,20 +30,20 @@ fn test_get_set_reset_extend() {
   \"shell.homepage\": \"https://google.com\"\
 }";
 
-    assert_eq!(*get_pref("test"), PrefValue::Missing);
-    set_pref("test", PrefValue::String("hi".to_owned()));
-    assert_eq!(*get_pref("test"), PrefValue::String("hi".to_owned()));
-    assert_eq!(*get_pref("shell.homepage"), PrefValue::String("http://servo.org".to_owned()));
-    set_pref("shell.homepage", PrefValue::Boolean(true));
-    assert_eq!(*get_pref("shell.homepage"), PrefValue::Boolean(true));
-    reset_pref("shell.homepage");
-    assert_eq!(*get_pref("shell.homepage"), PrefValue::String("http://servo.org".to_owned()));
+    assert_eq!(*PREFS.get("test"), PrefValue::Missing);
+    PREFS.set("test", PrefValue::String("hi".to_owned()));
+    assert_eq!(*PREFS.get("test"), PrefValue::String("hi".to_owned()));
+    assert_eq!(*PREFS.get("shell.homepage"), PrefValue::String("http://servo.org".to_owned()));
+    PREFS.set("shell.homepage", PrefValue::Boolean(true));
+    assert_eq!(*PREFS.get("shell.homepage"), PrefValue::Boolean(true));
+    PREFS.reset("shell.homepage");
+    assert_eq!(*PREFS.get("shell.homepage"), PrefValue::String("http://servo.org".to_owned()));
 
     let extension = read_prefs_from_file(json_str.as_bytes()).unwrap();
-    extend_prefs(extension);
-    assert_eq!(*get_pref("shell.homepage"), PrefValue::String("https://google.com".to_owned()));
-    assert_eq!(*get_pref("layout.writing-mode.enabled"), PrefValue::Boolean(true));
-    assert_eq!(*get_pref("extra.stuff"), PrefValue::Boolean(false));
+    PREFS.extend(extension);
+    assert_eq!(*PREFS.get("shell.homepage"), PrefValue::String("https://google.com".to_owned()));
+    assert_eq!(*PREFS.get("layout.writing-mode.enabled"), PrefValue::Boolean(true));
+    assert_eq!(*PREFS.get("extra.stuff"), PrefValue::Boolean(false));
 }
 
 #[test]