diff --git a/Cargo.lock b/Cargo.lock
index b998175a666..59cc45d04a9 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1587,7 +1587,7 @@ dependencies = [
  "fnv 1.0.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "futures 0.1.23 (registry+https://github.com/rust-lang/crates.io-index)",
  "http 0.1.13 (registry+https://github.com/rust-lang/crates.io-index)",
- "indexmap 1.0.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "indexmap 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "log 0.4.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "slab 0.4.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "string 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -1819,7 +1819,7 @@ dependencies = [
 
 [[package]]
 name = "indexmap"
-version = "1.0.1"
+version = "1.0.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
 [[package]]
@@ -3246,6 +3246,7 @@ dependencies = [
  "hyper 0.12.14 (registry+https://github.com/rust-lang/crates.io-index)",
  "hyper_serde 0.9.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "image 0.20.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "indexmap 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "ipc-channel 0.11.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "itertools 0.7.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "jstraceable_derive 0.0.1",
@@ -4950,7 +4951,7 @@ dependencies = [
 "checksum idna 0.1.4 (registry+https://github.com/rust-lang/crates.io-index)" = "014b298351066f1512874135335d62a789ffe78a9974f94b43ed5621951eaf7d"
 "checksum image 0.20.1 (registry+https://github.com/rust-lang/crates.io-index)" = "44665b4395d1844c96e7dc8ed5754782a1cdfd9ef458a80bbe45702681450504"
 "checksum immeta 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)" = "7371aa3c98fad60de2d9b517e2e1ed45593c32b0c77249310fa507749a2a318b"
-"checksum indexmap 1.0.1 (registry+https://github.com/rust-lang/crates.io-index)" = "08173ba1e906efb6538785a8844dd496f5d34f0a2d88038e95195172fc667220"
+"checksum indexmap 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)" = "7e81a7c05f79578dbc15793d8b619db9ba32b4577003ef3af1a91c416798c58d"
 "checksum inflate 0.4.3 (registry+https://github.com/rust-lang/crates.io-index)" = "6f53b811ee8e2057ccf9643ca6b4277de90efaf5e61e55fd5254576926bb4245"
 "checksum influent 0.5.0 (registry+https://github.com/rust-lang/crates.io-index)" = "8f06f65fa332019cbf57b927cd5a5da53cfce506109f38312fd597745a8a48c0"
 "checksum io-surface 0.11.1 (registry+https://github.com/rust-lang/crates.io-index)" = "5f9a33981dff54baaff80f4decb487a65d148a3c00facc97820d0f09128f74dd"
diff --git a/components/script/Cargo.toml b/components/script/Cargo.toml
index ed8a0eb3b43..071c429d584 100644
--- a/components/script/Cargo.toml
+++ b/components/script/Cargo.toml
@@ -61,6 +61,7 @@ http = "0.1"
 hyper = "0.12"
 hyper_serde = "0.9"
 image = "0.20"
+indexmap = "1.0.2"
 ipc-channel = "0.11"
 itertools = "0.7.6"
 jstraceable_derive = {path = "../jstraceable_derive"}
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) {