--- a/browser/modules/ContentWebRTC.jsm
+++ b/browser/modules/ContentWebRTC.jsm
@@ -256,18 +256,18 @@ function forgetPendingListsEventually(aC
     return;
   }
   aContentWindow.pendingGetUserMediaRequests = null;
   aContentWindow.pendingPeerConnectionRequests = null;
   aContentWindow.removeEventListener("unload", ContentWebRTC);
 }
 
 function updateIndicators() {
-  let contentWindowSupportsArray = MediaManagerService.activeMediaCaptureWindows;
-  let count = contentWindowSupportsArray.Count();
+  let contentWindowArray = MediaManagerService.activeMediaCaptureWindows;
+  let count = contentWindowArray.length;
 
   let state = {
     showGlobalIndicator: count > 0,
     showCameraIndicator: false,
     showMicrophoneIndicator: false,
     showScreenSharingIndicator: ""
   };
 
@@ -275,17 +275,17 @@ function updateIndicators() {
                .getService(Ci.nsIMessageSender);
   cpmm.sendAsyncMessage("webrtc:UpdatingIndicators");
 
   // If several iframes in the same page use media streams, it's possible to
   // have the same top level window several times. We use a Set to avoid
   // sending duplicate notifications.
   let contentWindows = new Set();
   for (let i = 0; i < count; ++i) {
-    contentWindows.add(contentWindowSupportsArray.GetElementAt(i).top);
+    contentWindows.add(contentWindowArray.queryElementAt(i, Ci.nsISupports).top);
   }
 
   for (let contentWindow of contentWindows) {
     let tabState = getTabStateForContentWindow(contentWindow);
     if (tabState.camera)
       state.showCameraIndicator = true;
     if (tabState.microphone)
       state.showMicrophoneIndicator = true;

--- a/dom/media/MediaManager.cpp
+++ b/dom/media/MediaManager.cpp
@@ -5,16 +5,17 @@
  * You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #include "MediaManager.h"
 
 #include "MediaStreamGraph.h"
 #include "mozilla/dom/MediaStreamTrack.h"
 #include "GetUserMediaRequest.h"
 #include "MediaStreamListener.h"
+#include "nsArray.h"
 #include "nsContentUtils.h"
 #include "nsHashPropertyBag.h"
 #ifdef MOZ_WIDGET_GONK
 #include "nsIAudioManager.h"
 #endif
 #include "nsIEventTarget.h"
 #include "nsIUUIDGenerator.h"
 #include "nsIScriptGlobalObject.h"
@@ -3128,24 +3129,21 @@ MediaManager::Observe(nsISupports* aSubj
     return NS_OK;
   }
 #endif
 
   return NS_OK;
 }
 
 nsresult
-MediaManager::GetActiveMediaCaptureWindows(nsISupportsArray** aArray)
+MediaManager::GetActiveMediaCaptureWindows(nsIArray** aArray)
 {
   MOZ_ASSERT(aArray);
-  nsISupportsArray* array;
-  nsresult rv = NS_NewISupportsArray(&array); // AddRefs
-  if (NS_FAILED(rv)) {
-    return rv;
-  }
+
+  nsCOMPtr<nsIMutableArray> array = nsArray::Create();
 
   for (auto iter = mActiveWindows.Iter(); !iter.Done(); iter.Next()) {
     const uint64_t& id = iter.Key();
     StreamListeners* listeners = iter.UserData();
 
     nsPIDOMWindowInner* window =
       nsGlobalWindow::GetInnerWindowWithId(id)->AsInner();
     MOZ_ASSERT(window);
@@ -3166,21 +3164,21 @@ MediaManager::GetActiveMediaCaptureWindo
             listener->CapturingScreen() || listener->CapturingWindow() ||
             listener->CapturingApplication()) {
           capturing = true;
           break;
         }
       }
     }
     if (capturing) {
-      array->AppendElement(window);
+      array->AppendElement(window, /*weak =*/ false);
     }
   }
 
-  *aArray = array;
+  array.forget(aArray);
   return NS_OK;
 }
 
 // XXX flags might be better...
 struct CaptureWindowStateData {
   bool *mVideo;
   bool *mAudio;
   bool *mScreenShare;
@@ -3329,43 +3327,43 @@ MediaManager::IterateWindowListeners(nsP
     }
   }
 }
 
 
 void
 MediaManager::StopMediaStreams()
 {
-  nsCOMPtr<nsISupportsArray> array;
+  nsCOMPtr<nsIArray> array;
   GetActiveMediaCaptureWindows(getter_AddRefs(array));
   uint32_t len;
-  array->Count(&len);
+  array->GetLength(&len);
   for (uint32_t i = 0; i < len; i++) {
-    nsCOMPtr<nsISupports> window;
-    array->GetElementAt(i, getter_AddRefs(window));
-    nsCOMPtr<nsPIDOMWindowInner> win(do_QueryInterface(window));
+    nsCOMPtr<nsPIDOMWindowInner> win;
+    array->QueryElementAt(i, NS_GET_IID(nsPIDOMWindowInner),
+                          getter_AddRefs(win));
     if (win) {
       OnNavigation(win->WindowID());
     }
   }
 }
 
 bool
 MediaManager::IsActivelyCapturingOrHasAPermission(uint64_t aWindowId)
 {
   // Does page currently have a gUM stream active?
 
-  nsCOMPtr<nsISupportsArray> array;
+  nsCOMPtr<nsIArray> array;
   GetActiveMediaCaptureWindows(getter_AddRefs(array));
   uint32_t len;
-  array->Count(&len);
+  array->GetLength(&len);
   for (uint32_t i = 0; i < len; i++) {
-    nsCOMPtr<nsISupports> window;
-    array->GetElementAt(i, getter_AddRefs(window));
-    nsCOMPtr<nsPIDOMWindowInner> win(do_QueryInterface(window));
+    nsCOMPtr<nsPIDOMWindowInner> win;
+    array->QueryElementAt(i, NS_GET_IID(nsPIDOMWindowInner),
+                          getter_AddRefs(win));
     if (win && win->WindowID() == aWindowId) {
       return true;
     }
   }
 
   // Or are persistent permissions (audio or video) granted?
 
   auto* window = nsGlobalWindow::GetInnerWindowWithId(aWindowId);

--- a/dom/media/nsIMediaManager.idl
+++ b/dom/media/nsIMediaManager.idl
@@ -1,27 +1,27 @@
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this file,
  * You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #include "nsISupports.idl"
 
-interface nsISupportsArray;
+interface nsIArray;
 interface nsIDOMWindow;
 
 %{C++
 #define NS_MEDIAMANAGERSERVICE_CID {0xabc622ea, 0x9655, 0x4123, {0x80, 0xd9, 0x22, 0x62, 0x1b, 0xdd, 0x54, 0x65}}
 #define MEDIAMANAGERSERVICE_CONTRACTID "@mozilla.org/mediaManagerService;1"
 %}
 
 [scriptable, builtinclass, uuid(24b23e01-33fd-401f-ba25-6e52658750b0)]
 interface nsIMediaManagerService : nsISupports
 {
   /* return a array of inner windows that have active captures */
-  readonly attribute nsISupportsArray activeMediaCaptureWindows;
+  readonly attribute nsIArray activeMediaCaptureWindows;
 
   /* Get the capture state for the given window and all descendant windows (iframes, etc) */
   void mediaCaptureWindowState(in nsIDOMWindow aWindow, out boolean aVideo, out boolean aAudio,
                                [optional] out boolean aScreenShare, [optional] out boolean aWindowShare,
                                [optional] out boolean aAppShare, [optional] out boolean aBrowserShare);
 
   /* Clear per-orgin list of persistent DeviceIds stored for enumerateDevices
      sinceTime is milliseconds since 1 January 1970 00:00:00 UTC. 0 = clear all */

--- a/mobile/android/chrome/content/WebrtcUI.js
+++ b/mobile/android/chrome/content/WebrtcUI.js
@@ -53,17 +53,17 @@ var WebrtcUI = {
       }
     } else if (aTopic === "VideoCapture:Resumed") {
       this.notify();
     }
   },
 
   notify: function() {
     let windows = MediaManagerService.activeMediaCaptureWindows;
-    let count = windows.Count();
+    let count = windows.length;
     let msg = {};
     if (count == 0) {
       if (this._notificationId) {
         Notifications.cancel(this._notificationId);
         this._notificationId = null;
       }
     } else {
       let notificationOptions = {
@@ -71,17 +71,17 @@ var WebrtcUI = {
         when: null, // hide the date row
         light: [0xFF9500FF, 1000, 1000],
         ongoing: true
       };
 
       let cameraActive = false;
       let audioActive = false;
       for (let i = 0; i < count; i++) {
-        let win = windows.GetElementAt(i);
+        let win = windows.queryElementAt(i, Ci.nsIDOMWindow);
         let hasAudio = {};
         let hasVideo = {};
         MediaManagerService.mediaCaptureWindowState(win, hasVideo, hasAudio);
         if (hasVideo.value) cameraActive = true;
         if (hasAudio.value) audioActive = true;
       }
 
       if (cameraActive && audioActive) {