Added a TopLevelBrowsingContextId type.

7 files changed, 164 insertions, 62 deletions

diff --git a/components/script/dom/bindings/trace.rs b/components/script/dom/bindings/trace.rs
index 3b96d954dcb..dca1b0e2ea5 100644
--- a/components/script/dom/bindings/trace.rs
+++ b/components/script/dom/bindings/trace.rs
@@ -58,7 +58,7 @@ use js::glue::{CallObjectTracer, CallValueTracer};
 use js::jsapi::{GCTraceKindToAscii, Heap, JSObject, JSTracer, TraceKind};
 use js::jsval::JSVal;
 use js::rust::Runtime;
-use msg::constellation_msg::{BrowsingContextId, FrameType, PipelineId};
+use msg::constellation_msg::{BrowsingContextId, FrameType, PipelineId, TopLevelBrowsingContextId};
 use net_traits::{Metadata, NetworkError, ReferrerPolicy, ResourceThreads};
 use net_traits::filemanager_thread::RelativePos;
 use net_traits::image::base::{Image, ImageMetadata};
@@ -336,7 +336,8 @@ unsafe_no_jsmanaged_fields!(TrustedPromise);
 unsafe_no_jsmanaged_fields!(PropertyDeclarationBlock);
 // These three are interdependent, if you plan to put jsmanaged data
 // in one of these make sure it is propagated properly to containing structs
-unsafe_no_jsmanaged_fields!(DocumentActivity, BrowsingContextId, FrameType, WindowSizeData, WindowSizeType, PipelineId);
+unsafe_no_jsmanaged_fields!(DocumentActivity, WindowSizeData, WindowSizeType);
+unsafe_no_jsmanaged_fields!(BrowsingContextId, FrameType, PipelineId, TopLevelBrowsingContextId);
 unsafe_no_jsmanaged_fields!(TimerEventId, TimerSource);
 unsafe_no_jsmanaged_fields!(TimelineMarkerType);
 unsafe_no_jsmanaged_fields!(WorkerId);
diff --git a/components/script/dom/dedicatedworkerglobalscope.rs b/components/script/dom/dedicatedworkerglobalscope.rs
index 6b73df12dfc..f4de73747c4 100644
--- a/components/script/dom/dedicatedworkerglobalscope.rs
+++ b/components/script/dom/dedicatedworkerglobalscope.rs
@@ -27,7 +27,7 @@ use js::jsapi::{HandleValue, JS_SetInterruptCallback};
 use js::jsapi::{JSAutoCompartment, JSContext};
 use js::jsval::UndefinedValue;
 use js::rust::Runtime;
-use msg::constellation_msg::BrowsingContextId;
+use msg::constellation_msg::TopLevelBrowsingContextId;
 use net_traits::{IpcSend, load_whole_resource};
 use net_traits::request::{CredentialsMode, Destination, RequestInit, Type as RequestType};
 use script_runtime::{CommonScriptMsg, ScriptChan, ScriptPort, StackRootTLS, get_reports, new_rt_and_cx};
@@ -159,13 +159,13 @@ impl DedicatedWorkerGlobalScope {
                             closing: Arc<AtomicBool>) {
         let serialized_worker_url = worker_url.to_string();
         let name = format!("WebWorker for {}", serialized_worker_url);
-        let top_level_browsing_context_id = BrowsingContextId::installed();
+        let top_level_browsing_context_id = TopLevelBrowsingContextId::installed();
 
         thread::Builder::new().name(name).spawn(move || {
             thread_state::initialize(thread_state::SCRIPT | thread_state::IN_WORKER);
 
             if let Some(top_level_browsing_context_id) = top_level_browsing_context_id {
-                BrowsingContextId::install(top_level_browsing_context_id);
+                TopLevelBrowsingContextId::install(top_level_browsing_context_id);
             }
 
             let roots = RootCollection::new();
diff --git a/components/script/dom/document.rs b/components/script/dom/document.rs
index 3bca1dcee9e..378dee975fa 100644
--- a/components/script/dom/document.rs
+++ b/components/script/dom/document.rs
@@ -100,7 +100,7 @@ use ipc_channel::ipc::{self, IpcSender};
 use js::jsapi::{JSContext, JSObject, JSRuntime};
 use js::jsapi::JS_GetRuntime;
 use msg::constellation_msg::{ALT, CONTROL, SHIFT, SUPER};
-use msg::constellation_msg::{BrowsingContextId, Key, KeyModifiers, KeyState};
+use msg::constellation_msg::{BrowsingContextId, Key, KeyModifiers, KeyState, TopLevelBrowsingContextId};
 use net_traits::{FetchResponseMsg, IpcSend, ReferrerPolicy};
 use net_traits::CookieSource::NonHTTP;
 use net_traits::CoreResourceMsg::{GetCookiesForUrl, SetCookiesForUrl};
@@ -1899,7 +1899,21 @@ impl Document {
     /// Find an iframe element in the document.
     pub fn find_iframe(&self, browsing_context_id: BrowsingContextId) -> Option<Root<HTMLIFrameElement>> {
         self.iter_iframes()
-            .find(|node| node.browsing_context_id() == browsing_context_id)
+            .find(|node| node.browsing_context_id() == Some(browsing_context_id))
+    }
+
+    /// Find a mozbrowser iframe element in the document.
+    pub fn find_mozbrowser_iframe(&self,
+                                  top_level_browsing_context_id: TopLevelBrowsingContextId)
+                                  -> Option<Root<HTMLIFrameElement>>
+    {
+        match self.find_iframe(BrowsingContextId::from(top_level_browsing_context_id)) {
+            None => None,
+            Some(iframe) => {
+                assert!(iframe.Mozbrowser());
+                Some(iframe)
+            },
+        }
     }
 
     pub fn get_dom_loading(&self) -> u64 {
diff --git a/components/script/dom/htmliframeelement.rs b/components/script/dom/htmliframeelement.rs
index 8334b4cb421..00755213c75 100644
--- a/components/script/dom/htmliframeelement.rs
+++ b/components/script/dom/htmliframeelement.rs
@@ -40,7 +40,7 @@ use html5ever::{LocalName, Prefix};
 use ipc_channel::ipc;
 use js::jsapi::{JSAutoCompartment, JSContext, MutableHandleValue};
 use js::jsval::{NullValue, UndefinedValue};
-use msg::constellation_msg::{FrameType, BrowsingContextId, PipelineId, TraversalDirection};
+use msg::constellation_msg::{FrameType, BrowsingContextId, PipelineId, TopLevelBrowsingContextId, TraversalDirection};
 use net_traits::response::HttpsState;
 use script_layout_interface::message::ReflowQueryType;
 use script_thread::{ScriptThread, Runnable};
@@ -84,7 +84,8 @@ enum ProcessingMode {
 #[dom_struct]
 pub struct HTMLIFrameElement {
     htmlelement: HTMLElement,
-    browsing_context_id: BrowsingContextId,
+    top_level_browsing_context_id: Cell<Option<TopLevelBrowsingContextId>>,
+    browsing_context_id: Cell<Option<BrowsingContextId>>,
     pipeline_id: Cell<Option<PipelineId>>,
     pending_pipeline_id: Cell<Option<PipelineId>>,
     sandbox: MutNullableJS<DOMTokenList>,
@@ -112,13 +113,6 @@ impl HTMLIFrameElement {
         }).unwrap_or_else(|| ServoUrl::parse("about:blank").unwrap())
     }
 
-    pub fn generate_new_pipeline_id(&self) -> (Option<PipelineId>, PipelineId) {
-        let old_pipeline_id = self.pipeline_id.get();
-        let new_pipeline_id = PipelineId::new();
-        debug!("Frame {} created pipeline {}.", self.browsing_context_id, new_pipeline_id);
-        (old_pipeline_id, new_pipeline_id)
-    }
-
     pub fn navigate_or_reload_child_browsing_context(&self,
                                                      load_data: Option<LoadData>,
                                                      nav_type: NavigationType,
@@ -129,6 +123,16 @@ impl HTMLIFrameElement {
             IFrameUnsandboxed
         };
 
+        let browsing_context_id = match self.browsing_context_id() {
+            None => return warn!("Navigating unattached iframe."),
+            Some(id) => id,
+        };
+
+        let top_level_browsing_context_id = match self.top_level_browsing_context_id() {
+            None => return warn!("Navigating unattached iframe."),
+            Some(id) => id,
+        };
+
         let document = document_from_node(self);
 
         let mut load_blocker = self.load_blocker.borrow_mut();
@@ -144,7 +148,8 @@ impl HTMLIFrameElement {
         }
 
         let window = window_from_node(self);
-        let (old_pipeline_id, new_pipeline_id) = self.generate_new_pipeline_id();
+        let old_pipeline_id = self.pipeline_id();
+        let new_pipeline_id = PipelineId::new();
         self.pending_pipeline_id.set(Some(new_pipeline_id));
         let private_iframe = self.privatebrowsing();
         let frame_type = if self.Mozbrowser() { FrameType::MozBrowserIFrame } else { FrameType::IFrame };
@@ -152,7 +157,8 @@ impl HTMLIFrameElement {
         let global_scope = window.upcast::<GlobalScope>();
         let load_info = IFrameLoadInfo {
             parent_pipeline_id: global_scope.pipeline_id(),
-            browsing_context_id: self.browsing_context_id,
+            browsing_context_id: browsing_context_id,
+            top_level_browsing_context_id: top_level_browsing_context_id,
             new_pipeline_id: new_pipeline_id,
             is_private: private_iframe,
             frame_type: frame_type,
@@ -171,7 +177,8 @@ impl HTMLIFrameElement {
                 let new_layout_info = NewLayoutInfo {
                     parent_info: Some((global_scope.pipeline_id(), frame_type)),
                     new_pipeline_id: new_pipeline_id,
-                    browsing_context_id: self.browsing_context_id,
+                    browsing_context_id: browsing_context_id,
+                    top_level_browsing_context_id: top_level_browsing_context_id,
                     load_data: load_data.unwrap(),
                     pipeline_port: pipeline_receiver,
                     content_process_shutdown_chan: None,
@@ -246,11 +253,29 @@ impl HTMLIFrameElement {
         // Synchronously create a new context and navigate it to about:blank.
         let url = ServoUrl::parse("about:blank").unwrap();
         let document = document_from_node(self);
-        let pipeline_id = Some(window_from_node(self).upcast::<GlobalScope>().pipeline_id());
+        let window = window_from_node(self);
+        let pipeline_id = Some(window.upcast::<GlobalScope>().pipeline_id());
         let load_data = LoadData::new(url, pipeline_id, document.get_referrer_policy(), Some(document.url().clone()));
+        let (browsing_context_id, top_level_browsing_context_id) = if self.Mozbrowser() {
+            let top_level_browsing_context_id = TopLevelBrowsingContextId::new();
+            (BrowsingContextId::from(top_level_browsing_context_id), top_level_browsing_context_id)
+        } else {
+            (BrowsingContextId::new(), window.window_proxy().top_level_browsing_context_id())
+        };
+        self.pipeline_id.set(None);
+        self.pending_pipeline_id.set(None);
+        self.top_level_browsing_context_id.set(Some(top_level_browsing_context_id));
+        self.browsing_context_id.set(Some(browsing_context_id));
         self.navigate_or_reload_child_browsing_context(Some(load_data), NavigationType::InitialAboutBlank, false);
     }
 
+    fn destroy_nested_browsing_context(&self) {
+        self.pipeline_id.set(None);
+        self.pending_pipeline_id.set(None);
+        self.top_level_browsing_context_id.set(None);
+        self.browsing_context_id.set(None);
+    }
+
     pub fn update_pipeline_id(&self, new_pipeline_id: PipelineId, reason: UpdatePipelineIdReason) {
         if self.pending_pipeline_id.get() != Some(new_pipeline_id) && reason == UpdatePipelineIdReason::Navigation {
             return;
@@ -277,7 +302,8 @@ impl HTMLIFrameElement {
                      document: &Document) -> HTMLIFrameElement {
         HTMLIFrameElement {
             htmlelement: HTMLElement::new_inherited(local_name, prefix, document),
-            browsing_context_id: BrowsingContextId::new(),
+            browsing_context_id: Cell::new(None),
+            top_level_browsing_context_id: Cell::new(None),
             pipeline_id: Cell::new(None),
             pending_pipeline_id: Cell::new(None),
             sandbox: Default::default(),
@@ -302,8 +328,13 @@ impl HTMLIFrameElement {
     }
 
     #[inline]
-    pub fn browsing_context_id(&self) -> BrowsingContextId {
-        self.browsing_context_id
+    pub fn browsing_context_id(&self) -> Option<BrowsingContextId> {
+        self.browsing_context_id.get()
+    }
+
+    #[inline]
+    pub fn top_level_browsing_context_id(&self) -> Option<TopLevelBrowsingContextId> {
+        self.top_level_browsing_context_id.get()
     }
 
     pub fn change_visibility_status(&self, visibility: bool) {
@@ -364,7 +395,7 @@ impl HTMLIFrameElement {
 
 pub trait HTMLIFrameElementLayoutMethods {
     fn pipeline_id(&self) -> Option<PipelineId>;
-    fn browsing_context_id(&self) -> BrowsingContextId;
+    fn browsing_context_id(&self) -> Option<BrowsingContextId>;
     fn get_width(&self) -> LengthOrPercentageOrAuto;
     fn get_height(&self) -> LengthOrPercentageOrAuto;
 }
@@ -380,9 +411,9 @@ impl HTMLIFrameElementLayoutMethods for LayoutJS<HTMLIFrameElement> {
 
     #[inline]
     #[allow(unsafe_code)]
-    fn browsing_context_id(&self) -> BrowsingContextId {
+    fn browsing_context_id(&self) -> Option<BrowsingContextId> {
         unsafe {
-            (*self.unsafe_get()).browsing_context_id
+            (*self.unsafe_get()).browsing_context_id.get()
         }
     }
 
@@ -541,7 +572,8 @@ impl HTMLIFrameElementMethods for HTMLIFrameElement {
 
     // https://html.spec.whatwg.org/multipage/#dom-iframe-contentwindow
     fn GetContentWindow(&self) -> Option<Root<WindowProxy>> {
-        self.pipeline_id.get().and_then(|_| ScriptThread::find_window_proxy(self.browsing_context_id))
+        self.browsing_context_id.get()
+            .and_then(|browsing_context_id| ScriptThread::find_window_proxy(browsing_context_id))
     }
 
     // https://html.spec.whatwg.org/multipage/#dom-iframe-contentdocument
@@ -711,7 +743,7 @@ impl VirtualMethods for HTMLIFrameElement {
                 // is in a document tree and has a browsing context, which is what causes
                 // the child browsing context to be created.
                 if self.upcast::<Node>().is_in_doc_with_browsing_context() {
-                    debug!("iframe {} src set while in browsing context.", self.browsing_context_id);
+                    debug!("iframe src set while in browsing context.");
                     self.process_the_iframe_attributes(ProcessingMode::NotFirstTime);
                 }
             },
@@ -740,7 +772,7 @@ impl VirtualMethods for HTMLIFrameElement {
         // to the newly-created browsing context, and then process the
         // iframe attributes for the "first time"."
         if self.upcast::<Node>().is_in_doc_with_browsing_context() {
-            debug!("iframe {} bound to browsing context.", self.browsing_context_id);
+            debug!("iframe bound to browsing context.");
             debug_assert!(tree_in_doc, "is_in_doc_with_bc, but not tree_in_doc");
             self.create_nested_browsing_context();
             self.process_the_iframe_attributes(ProcessingMode::FirstTime);
@@ -754,13 +786,18 @@ impl VirtualMethods for HTMLIFrameElement {
         LoadBlocker::terminate(&mut blocker);
 
         // https://html.spec.whatwg.org/multipage/#a-browsing-context-is-discarded
-        debug!("Unbinding frame {}.", self.browsing_context_id);
         let window = window_from_node(self);
         let (sender, receiver) = ipc::channel().unwrap();
 
         // Ask the constellation to remove the iframe, and tell us the
         // pipeline ids of the closed pipelines.
-        let msg = ConstellationMsg::RemoveIFrame(self.browsing_context_id, sender);
+        let browsing_context_id = match self.browsing_context_id() {
+            None => return warn!("Unbinding already unbound iframe."),
+            Some(id) => id,
+        };
+        debug!("Unbinding frame {}.", browsing_context_id);
+
+        let msg = ConstellationMsg::RemoveIFrame(browsing_context_id, sender);
         window.upcast::<GlobalScope>().constellation_chan().send(msg).unwrap();
         let exited_pipeline_ids = receiver.recv().unwrap();
 
@@ -769,9 +806,11 @@ impl VirtualMethods for HTMLIFrameElement {
         // when the `PipelineExit` message arrives.
         for exited_pipeline_id in exited_pipeline_ids {
             if let Some(exited_document) = ScriptThread::find_document(exited_pipeline_id) {
+                debug!("Discarding browsing context for pipeline {}", exited_pipeline_id);
                 exited_document.window().window_proxy().discard_browsing_context();
                 for exited_iframe in exited_document.iter_iframes() {
-                    exited_iframe.pipeline_id.set(None);
+                    debug!("Discarding nested browsing context");
+                    exited_iframe.destroy_nested_browsing_context();
                 }
             }
         }
@@ -781,8 +820,7 @@ impl VirtualMethods for HTMLIFrameElement {
         // the load doesn't think that it's a navigation, but instead
         // a new iframe. Without this, the constellation gets very
         // confused.
-        self.pipeline_id.set(None);
-        self.pending_pipeline_id.set(None);
+        self.destroy_nested_browsing_context();
     }
 }
 
diff --git a/components/script/dom/node.rs b/components/script/dom/node.rs
index ff3e5d64787..cc817587eda 100644
--- a/components/script/dom/node.rs
+++ b/components/script/dom/node.rs
@@ -1136,7 +1136,7 @@ impl LayoutNodeHelpers for LayoutJS<Node> {
     fn iframe_browsing_context_id(&self) -> BrowsingContextId {
         let iframe_element = self.downcast::<HTMLIFrameElement>()
             .expect("not an iframe element!");
-        iframe_element.browsing_context_id()
+        iframe_element.browsing_context_id().unwrap()
     }
 
     fn iframe_pipeline_id(&self) -> PipelineId {
diff --git a/components/script/dom/windowproxy.rs b/components/script/dom/windowproxy.rs
index e022e69a810..2578bb3b46c 100644
--- a/components/script/dom/windowproxy.rs
+++ b/components/script/dom/windowproxy.rs
@@ -30,6 +30,7 @@ use js::jsval::{UndefinedValue, PrivateValue};
 use js::rust::get_object_class;
 use msg::constellation_msg::BrowsingContextId;
 use msg::constellation_msg::PipelineId;
+use msg::constellation_msg::TopLevelBrowsingContextId;
 use std::cell::Cell;
 use std::ptr;
 
@@ -50,6 +51,10 @@ pub struct WindowProxy {
     /// of the container.
     browsing_context_id: BrowsingContextId,
 
+    /// The frame id of the top-level ancestor browsing context.
+    /// In the case that this is a top-level window, this is our id.
+    top_level_browsing_context_id: TopLevelBrowsingContextId,
+
     /// The pipeline id of the currently active document.
     /// May be None, when the currently active document is in another script thread.
     /// We do not try to keep the pipeline id for documents in other threads,
@@ -69,6 +74,7 @@ pub struct WindowProxy {
 
 impl WindowProxy {
     pub fn new_inherited(browsing_context_id: BrowsingContextId,
+                         top_level_browsing_context_id: TopLevelBrowsingContextId,
                          currently_active: Option<PipelineId>,
                          frame_element: Option<&Element>,
                          parent: Option<&WindowProxy>)
@@ -77,6 +83,7 @@ impl WindowProxy {
         WindowProxy {
             reflector: Reflector::new(),
             browsing_context_id: browsing_context_id,
+            top_level_browsing_context_id: top_level_browsing_context_id,
             currently_active: Cell::new(currently_active),
             discarded: Cell::new(false),
             frame_element: frame_element.map(JS::from_ref),
@@ -87,6 +94,7 @@ impl WindowProxy {
     #[allow(unsafe_code)]
     pub fn new(window: &Window,
                browsing_context_id: BrowsingContextId,
+               top_level_browsing_context_id: TopLevelBrowsingContextId,
                frame_element: Option<&Element>,
                parent: Option<&WindowProxy>)
                -> Root<WindowProxy>
@@ -107,7 +115,11 @@ impl WindowProxy {
 
             // Create a new browsing context.
             let current = Some(window.global().pipeline_id());
-            let mut window_proxy = box WindowProxy::new_inherited(browsing_context_id, current, frame_element, parent);
+            let mut window_proxy = box WindowProxy::new_inherited(browsing_context_id,
+                                                                  top_level_browsing_context_id,
+                                                                  current,
+                                                                  frame_element,
+                                                                  parent);
 
             // The window proxy owns the browsing context.
             // When we finalize the window proxy, it drops the browsing context it owns.
@@ -126,6 +138,7 @@ impl WindowProxy {
     #[allow(unsafe_code)]
     pub fn new_dissimilar_origin(global_to_clone_from: &GlobalScope,
                                  browsing_context_id: BrowsingContextId,
+                                 top_level_browsing_context_id: TopLevelBrowsingContextId,
                                  parent: Option<&WindowProxy>)
                                  -> Root<WindowProxy>
     {
@@ -136,7 +149,11 @@ impl WindowProxy {
             let cx = global_to_clone_from.get_cx();
 
             // Create a new browsing context.
-            let mut window_proxy = box WindowProxy::new_inherited(browsing_context_id, None, None, parent);
+            let mut window_proxy = box WindowProxy::new_inherited(browsing_context_id,
+                                                                  top_level_browsing_context_id,
+                                                                  None,
+                                                                  None,
+                                                                  parent);
 
             // Create a new dissimilar-origin window.
             let window = DissimilarOriginWindow::new(global_to_clone_from, &*window_proxy);
@@ -175,6 +192,10 @@ impl WindowProxy {
         self.browsing_context_id
     }
 
+    pub fn top_level_browsing_context_id(&self) -> TopLevelBrowsingContextId {
+        self.top_level_browsing_context_id
+    }
+
     pub fn frame_element(&self) -> Option<&Element> {
         self.frame_element.r()
     }
diff --git a/components/script/script_thread.rs b/components/script/script_thread.rs
index eeab44c4c71..d66baaeda81 100644
--- a/components/script/script_thread.rs
+++ b/components/script/script_thread.rs
@@ -73,7 +73,7 @@ use js::jsval::UndefinedValue;
 use js::rust::Runtime;
 use mem::heap_size_of_self_and_children;
 use microtask::{MicrotaskQueue, Microtask};
-use msg::constellation_msg::{BrowsingContextId, FrameType, PipelineId, PipelineNamespace};
+use msg::constellation_msg::{BrowsingContextId, FrameType, PipelineId, PipelineNamespace, TopLevelBrowsingContextId};
 use net_traits::{CoreResourceMsg, FetchMetadata, FetchResponseListener};
 use net_traits::{IpcSend, Metadata, ReferrerPolicy, ResourceThreads};
 use net_traits::image_cache::{ImageCache, PendingImageResponse};
@@ -143,8 +143,10 @@ pub unsafe fn trace_thread(tr: *mut JSTracer) {
 struct InProgressLoad {
     /// The pipeline which requested this load.
     pipeline_id: PipelineId,
-    /// The frame being loaded into.
+    /// The browsing context being loaded into.
     browsing_context_id: BrowsingContextId,
+    /// The top level ancestor browsing context.
+    top_level_browsing_context_id: TopLevelBrowsingContextId,
     /// The parent pipeline and frame type associated with this load, if any.
     parent_info: Option<(PipelineId, FrameType)>,
     /// The current window size associated with this pipeline.
@@ -165,6 +167,7 @@ impl InProgressLoad {
     /// Create a new InProgressLoad object.
     fn new(id: PipelineId,
            browsing_context_id: BrowsingContextId,
+           top_level_browsing_context_id: TopLevelBrowsingContextId,
            parent_info: Option<(PipelineId, FrameType)>,
            layout_chan: Sender<message::Msg>,
            window_size: Option<WindowSizeData>,
@@ -173,6 +176,7 @@ impl InProgressLoad {
         InProgressLoad {
             pipeline_id: id,
             browsing_context_id: browsing_context_id,
+            top_level_browsing_context_id: top_level_browsing_context_id,
             parent_info: parent_info,
             layout_chan: layout_chan,
             window_size: window_size,
@@ -548,11 +552,12 @@ impl ScriptThreadFactory for ScriptThread {
         thread::Builder::new().name(format!("ScriptThread {:?}", state.id)).spawn(move || {
             thread_state::initialize(thread_state::SCRIPT);
             PipelineNamespace::install(state.pipeline_namespace_id);
-            BrowsingContextId::install(state.top_level_browsing_context_id);
+            TopLevelBrowsingContextId::install(state.top_level_browsing_context_id);
             let roots = RootCollection::new();
             let _stack_roots_tls = StackRootTLS::new(&roots);
             let id = state.id;
             let browsing_context_id = state.browsing_context_id;
+            let top_level_browsing_context_id = state.top_level_browsing_context_id;
             let parent_info = state.parent_info;
             let mem_profiler_chan = state.mem_profiler_chan.clone();
             let window_size = state.window_size;
@@ -567,7 +572,7 @@ impl ScriptThreadFactory for ScriptThread {
             let mut failsafe = ScriptMemoryFailsafe::new(&script_thread);
 
             let origin = MutableOrigin::new(load_data.url.origin());
-            let new_load = InProgressLoad::new(id, browsing_context_id, parent_info,
+            let new_load = InProgressLoad::new(id, browsing_context_id, top_level_browsing_context_id, parent_info,
                                                layout_chan, window_size, load_data.url.clone(), origin);
             script_thread.start_page_load(new_load, load_data);
 
@@ -1117,10 +1122,10 @@ impl ScriptThread {
             ConstellationControlMsg::PostMessage(pipeline_id, origin, data) =>
                 self.handle_post_message_msg(pipeline_id, origin, data),
             ConstellationControlMsg::MozBrowserEvent(parent_pipeline_id,
-                                                     browsing_context_id,
+                                                     top_level_browsing_context_id,
                                                      event) =>
                 self.handle_mozbrowser_event_msg(parent_pipeline_id,
-                                                 browsing_context_id,
+                                                 top_level_browsing_context_id,
                                                  event),
             ConstellationControlMsg::UpdatePipelineId(parent_pipeline_id,
                                                       browsing_context_id,
@@ -1344,6 +1349,7 @@ impl ScriptThread {
             parent_info,
             new_pipeline_id,
             browsing_context_id,
+            top_level_browsing_context_id,
             load_data,
             window_size,
             pipeline_port,
@@ -1379,9 +1385,14 @@ impl ScriptThread {
         };
 
         // Kick off the fetch for the new resource.
-        let new_load = InProgressLoad::new(new_pipeline_id, browsing_context_id, parent_info,
-                                           layout_chan, window_size,
-                                           load_data.url.clone(), origin);
+        let new_load = InProgressLoad::new(new_pipeline_id,
+                                           browsing_context_id,
+                                           top_level_browsing_context_id,
+                                           parent_info,
+                                           layout_chan,
+                                           window_size,
+                                           load_data.url.clone(),
+                                           origin);
         if load_data.url.as_str() == "about:blank" {
             self.start_page_load_about_blank(new_load);
         } else {
@@ -1495,17 +1506,18 @@ impl ScriptThread {
     /// https://developer.mozilla.org/en-US/docs/Web/Events/mozbrowserloadstart
     fn handle_mozbrowser_event_msg(&self,
                                    parent_pipeline_id: PipelineId,
-                                   browsing_context_id: Option<BrowsingContextId>,
+                                   top_level_browsing_context_id: Option<TopLevelBrowsingContextId>,
                                    event: MozBrowserEvent) {
         let doc = match { self.documents.borrow().find_document(parent_pipeline_id) } {
             None => return warn!("Mozbrowser event after pipeline {} closed.", parent_pipeline_id),
             Some(doc) => doc,
         };
 
-        match browsing_context_id {
+        match top_level_browsing_context_id {
             None => doc.window().dispatch_mozbrowser_event(event),
-            Some(browsing_context_id) => match doc.find_iframe(browsing_context_id) {
-                None => warn!("Mozbrowser event after iframe {}/{} closed.", parent_pipeline_id, browsing_context_id),
+            Some(top_level_browsing_context_id) => match doc.find_mozbrowser_iframe(top_level_browsing_context_id) {
+                None => warn!("Mozbrowser event after iframe {}/{} closed.",
+                              parent_pipeline_id, top_level_browsing_context_id),
                 Some(frame_element) => frame_element.dispatch_mozbrowser_event(event),
             },
         }
@@ -1779,9 +1791,10 @@ impl ScriptThread {
     // construct a new dissimilar-origin browsing context, add it
     // to the `window_proxies` map, and return it.
     fn remote_window_proxy(&self,
-                               global_to_clone: &GlobalScope,
-                               pipeline_id: PipelineId)
-                               -> Option<Root<WindowProxy>>
+                           global_to_clone: &GlobalScope,
+                           top_level_browsing_context_id: TopLevelBrowsingContextId,
+                           pipeline_id: PipelineId)
+                           -> Option<Root<WindowProxy>>
     {
         let browsing_context_id = match self.ask_constellation_for_browsing_context_id(pipeline_id) {
             Some(browsing_context_id) => browsing_context_id,
@@ -1791,10 +1804,15 @@ impl ScriptThread {
             return Some(Root::from_ref(window_proxy));
         }
         let parent = match self.ask_constellation_for_parent_info(pipeline_id) {
-            Some((parent_id, FrameType::IFrame)) => self.remote_window_proxy(global_to_clone, parent_id),
+            Some((parent_id, FrameType::IFrame)) => self.remote_window_proxy(global_to_clone,
+                                                                             top_level_browsing_context_id,
+                                                                             parent_id),
             _ => None,
         };
-        let window_proxy = WindowProxy::new_dissimilar_origin(global_to_clone, browsing_context_id, parent.r());
+        let window_proxy = WindowProxy::new_dissimilar_origin(global_to_clone,
+                                                              browsing_context_id,
+                                                              top_level_browsing_context_id,
+                                                              parent.r());
         self.window_proxies.borrow_mut().insert(browsing_context_id, JS::from_ref(&*window_proxy));
         Some(window_proxy)
     }
@@ -1806,10 +1824,11 @@ impl ScriptThread {
     // construct a new similar-origin browsing context, add it
     // to the `window_proxies` map, and return it.
     fn local_window_proxy(&self,
-                              window: &Window,
-                              browsing_context_id: BrowsingContextId,
-                              parent_info: Option<(PipelineId, FrameType)>)
-                              -> Root<WindowProxy>
+                          window: &Window,
+                          browsing_context_id: BrowsingContextId,
+                          top_level_browsing_context_id: TopLevelBrowsingContextId,
+                          parent_info: Option<(PipelineId, FrameType)>)
+                          -> Root<WindowProxy>
     {
         if let Some(window_proxy) = self.window_proxies.borrow().get(&browsing_context_id) {
             window_proxy.set_currently_active(&*window);
@@ -1821,10 +1840,16 @@ impl ScriptThread {
         };
         let parent = match (parent_info, iframe.as_ref()) {
             (_, Some(iframe)) => Some(window_from_node(&**iframe).window_proxy()),
-            (Some((parent_id, FrameType::IFrame)), _) => self.remote_window_proxy(window.upcast(), parent_id),
+            (Some((parent_id, FrameType::IFrame)), _) => self.remote_window_proxy(window.upcast(),
+                                                                                  top_level_browsing_context_id,
+                                                                                  parent_id),
             _ => None,
         };
-        let window_proxy = WindowProxy::new(&window, browsing_context_id, iframe.r().map(Castable::upcast), parent.r());
+        let window_proxy = WindowProxy::new(&window,
+                                            browsing_context_id,
+                                            top_level_browsing_context_id,
+                                            iframe.r().map(Castable::upcast),
+                                            parent.r());
         self.window_proxies.borrow_mut().insert(browsing_context_id, JS::from_ref(&*window_proxy));
         window_proxy
     }
@@ -1882,7 +1907,10 @@ impl ScriptThread {
                                  self.webvr_thread.clone());
 
         // Initialize the browsing context for the window.
-        let window_proxy = self.local_window_proxy(&window, incomplete.browsing_context_id, incomplete.parent_info);
+        let window_proxy = self.local_window_proxy(&window,
+                                                   incomplete.browsing_context_id,
+                                                   incomplete.top_level_browsing_context_id,
+                                                   incomplete.parent_info);
         window.init_window_proxy(&window_proxy);
 
         let last_modified = metadata.headers.as_ref().and_then(|headers| {