2 files changed, 22 insertions, 6 deletions
diff --git a/components/script/dom/bindings/mozmap.rs b/components/script/dom/bindings/mozmap.rs
index 9658d0c0d5e..db46debc58e 100644
--- a/components/script/dom/bindings/mozmap.rs
+++ b/components/script/dom/bindings/mozmap.rs
@@ -7,6 +7,7 @@
 use crate::dom::bindings::conversions::jsid_to_string;
 use crate::dom::bindings::error::report_pending_exception;
 use crate::dom::bindings::str::DOMString;
+use indexmap::IndexMap;
 use js::conversions::{ConversionResult, FromJSValConvertible, ToJSValConvertible};
 use js::jsapi::JSContext;
 use js::jsapi::JS_NewPlainObject;
@@ -22,28 +23,27 @@ use js::rust::wrappers::JS_GetPropertyById;
 use js::rust::HandleValue;
 use js::rust::IdVector;
 use js::rust::MutableHandleValue;
-use std::collections::HashMap;
 use std::ops::Deref;
 
 /// The `MozMap` (open-ended dictionary) type.
 #[derive(Clone, JSTraceable)]
 pub struct MozMap<T> {
-    map: HashMap<DOMString, T>,
+    map: IndexMap<DOMString, T>,
 }
 
 impl<T> MozMap<T> {
     /// Create an empty `MozMap`.
     pub fn new() -> Self {
         MozMap {
-            map: HashMap::new(),
+            map: IndexMap::new(),
         }
     }
 }
 
 impl<T> Deref for MozMap<T> {
-    type Target = HashMap<DOMString, T>;
+    type Target = IndexMap<DOMString, T>;
 
-    fn deref(&self) -> &HashMap<DOMString, T> {
+    fn deref(&self) -> &IndexMap<DOMString, T> {
         &self.map
     }
 }
@@ -82,7 +82,7 @@ where
             ));
         }
 
-        let mut map = HashMap::new();
+        let mut map = IndexMap::new();
         for id in &*ids {
             rooted!(in(cx) let id = *id);
 
diff --git a/components/script/dom/bindings/trace.rs b/components/script/dom/bindings/trace.rs
index 4fecf083737..ae1a9e6e3b4 100644
--- a/components/script/dom/bindings/trace.rs
+++ b/components/script/dom/bindings/trace.rs
@@ -61,6 +61,7 @@ use html5ever::{LocalName, Namespace, Prefix, QualName};
 use http::header::HeaderMap;
 use hyper::Method;
 use hyper::StatusCode;
+use indexmap::IndexMap;
 use ipc_channel::ipc::{IpcReceiver, IpcSender};
 use js::glue::{CallObjectTracer, CallValueTracer};
 use js::jsapi::{GCTraceKindToAscii, Heap, JSObject, JSTracer, TraceKind};
@@ -356,6 +357,21 @@ unsafe impl<K: Ord + JSTraceable, V: JSTraceable> JSTraceable for BTreeMap<K, V>
     }
 }
 
+unsafe impl<K, V, S> JSTraceable for IndexMap<K, V, S>
+where
+    K: Hash + Eq + JSTraceable,
+    V: JSTraceable,
+    S: BuildHasher,
+{
+    #[inline]
+    unsafe fn trace(&self, trc: *mut JSTracer) {
+        for (k, v) in &*self {
+            k.trace(trc);
+            v.trace(trc);
+        }
+    }
+}
+
 unsafe impl<A: JSTraceable, B: JSTraceable> JSTraceable for (A, B) {
     #[inline]
     unsafe fn trace(&self, trc: *mut JSTracer) {