diff --git a/dom/media/MediaManager.cpp b/dom/media/MediaManager.cpp
index 944e76783215..4441b3f6c9ad 100644
--- a/dom/media/MediaManager.cpp
+++ b/dom/media/MediaManager.cpp
@@ -2217,8 +2217,12 @@ void MediaManager::DeviceListChanged() {
   }
   mDeviceListChangeEvent.Notify();
 
-  // On some Windows machines, if we call EnumerateRawDevices immediately after
-  // receiving devicechange event, we would get an outdated devices list.
+  // Wait 200 ms, because
+  // A) on some Windows machines, if we call EnumerateRawDevices immediately
+  //    after receiving devicechange event, we'd get an outdated devices list.
+  // B) Waiting helps coalesce multiple calls on us into one, which can happen
+  //    if a device with both audio input and output is attached or removed.
+  //    We want to react & fire a devicechange event only once in that case.
 
   if (mDeviceChangeTimer) {
     mDeviceChangeTimer->Cancel();
@@ -2255,18 +2259,18 @@ void MediaManager::DeviceListChanged() {
               return;
             }
 
-            nsTArray<nsString> deviceIDs;
+            MediaManager::DeviceIdSet deviceIDs;
             for (auto& device : *devices) {
               nsString id;
               device->GetId(id);
-              if (!deviceIDs.Contains(id)) {
-                deviceIDs.AppendElement(id);
-              }
+              MOZ_ALWAYS_TRUE(deviceIDs.put(std::move(id)));
             }
-            // For any removed devices, notify their listeners cleanly that the
-            // source has stopped, so JS knows and usage indicators update.
-            for (auto& id : mDeviceIDs) {
-              if (deviceIDs.Contains(id)) {
+            // For any real removed cameras, microphones or speakers, notify
+            // their listeners cleanly that the source has stopped, so JS knows
+            // and usage indicators update.
+            for (auto iter = mDeviceIDs.iter(); !iter.done(); iter.next()) {
+              const auto& id = iter.get();
+              if (deviceIDs.has(id)) {
                 // Device has not been removed
                 continue;
               }
@@ -3127,7 +3131,8 @@ RefPtr<MediaManager::MgrPromise> MediaManager::EnumerateDevicesImpl(
           })
       ->Then(
           GetMainThreadSerialEventTarget(), __func__,
-          [aWindowId, originKey, aOutDevices](bool) {
+          [aWindowId, originKey, aVideoInputEnumType, aAudioInputEnumType,
+           aOutDevices](bool) {
             // Only run if window is still on our active list.
             MediaManager* mgr = MediaManager::GetIfExists();
             if (!mgr || !mgr->IsWindowStillActive(aWindowId)) {
@@ -3136,12 +3141,17 @@ RefPtr<MediaManager::MgrPromise> MediaManager::EnumerateDevicesImpl(
                   __func__);
             }
 
-            mgr->mDeviceIDs.Clear();
             for (auto& device : *aOutDevices) {
-              nsString id;
-              device->GetId(id);
-              if (!mgr->mDeviceIDs.Contains(id)) {
-                mgr->mDeviceIDs.AppendElement(id);
+              if (device->mKind == MediaDeviceKind::Audiooutput ||
+                  (device->mKind == MediaDeviceKind::Audioinput &&
+                   aAudioInputEnumType != DeviceEnumerationType::Fake &&
+                   device->GetMediaSource() == MediaSourceEnum::Microphone) ||
+                  (device->mKind == MediaDeviceKind::Videoinput &&
+                   aVideoInputEnumType != DeviceEnumerationType::Fake &&
+                   device->GetMediaSource() == MediaSourceEnum::Camera)) {
+                nsString id;
+                device->GetId(id);
+                MOZ_ALWAYS_TRUE(mgr->mDeviceIDs.put(std::move(id)));
               }
             }
 
@@ -3670,7 +3680,7 @@ void MediaManager::Shutdown() {
   mActiveCallbacks.Clear();
   mCallIds.Clear();
   mPendingGUMRequest.Clear();
-  mDeviceIDs.Clear();
+  mDeviceIDs.clear();
 #ifdef MOZ_WEBRTC
   StopWebRtcLog();
 #endif
diff --git a/dom/media/MediaManager.h b/dom/media/MediaManager.h
index 1169288c8a87..1659e55b7c2b 100644
--- a/dom/media/MediaManager.h
+++ b/dom/media/MediaManager.h
@@ -358,7 +358,21 @@ class MediaManager final : public nsIMediaManagerService, public nsIObserver {
   static StaticRefPtr<MediaManager> sSingleton;
   static StaticMutex sSingletonMutex;
 
-  nsTArray<nsString> mDeviceIDs;
+  struct nsStringHasher {
+    using Key = nsString;
+    using Lookup = nsString;
+
+    static HashNumber hash(const Lookup& aLookup) {
+      return HashString(aLookup.get());
+    }
+
+    static bool match(const Key& aKey, const Lookup& aLookup) {
+      return aKey == aLookup;
+    }
+  };
+
+  using DeviceIdSet = HashSet<nsString, nsStringHasher, InfallibleAllocPolicy>;
+  DeviceIdSet mDeviceIDs;
 
   // Connect/Disconnect on media thread only
   MediaEventListener mDeviceListChangeListener;
diff --git a/dom/media/webrtc/MediaEngine.h b/dom/media/webrtc/MediaEngine.h
index efce5b4a341b..75b39e843324 100644
--- a/dom/media/webrtc/MediaEngine.h
+++ b/dom/media/webrtc/MediaEngine.h
@@ -47,7 +47,9 @@ class MediaEngine {
 
   virtual void Shutdown() = 0;
 
-  virtual void SetFakeDeviceChangeEventsEnabled(bool aEnable) {}
+  virtual void SetFakeDeviceChangeEventsEnabled(bool aEnable) {
+    MOZ_DIAGNOSTIC_ASSERT(false, "Fake events may not have started/stopped");
+  }
 
   virtual MediaEventSource<void>& DeviceListChangeEvent() = 0;