--- a/dom/media/webrtc/MediaEngineDefault.cpp
+++ b/dom/media/webrtc/MediaEngineDefault.cpp
@@ -233,16 +233,20 @@ MediaEngineDefaultVideoSource::Start(con
   return NS_OK;
 }
 
 nsresult
 MediaEngineDefaultVideoSource::Stop(const RefPtr<const AllocationHandle>& aHandle)
 {
   AssertIsOnOwningThread();
 
+  if (mState == kStopped || mState == kAllocated) {
+    return NS_OK;
+  }
+
   MOZ_ASSERT(mState == kStarted);
   MOZ_ASSERT(mTimer);
   MOZ_ASSERT(mStream);
   MOZ_ASSERT(IsTrackIDExplicit(mTrackID));
 
   mTimer->Cancel();
   mTimer = nullptr;
 
@@ -493,19 +497,22 @@ MediaEngineDefaultAudioSource::Start(con
   return NS_OK;
 }
 
 nsresult
 MediaEngineDefaultAudioSource::Stop(const RefPtr<const AllocationHandle>& aHandle)
 {
   AssertIsOnOwningThread();
 
+  if (mState == kStopped || mState == kAllocated) {
+    return NS_OK;
+  }
+
   MOZ_ASSERT(mState == kStarted);
 
-
   MutexAutoLock lock(mMutex);
   mState = kStopped;
   return NS_OK;
 }
 
 nsresult
 MediaEngineDefaultAudioSource::Reconfigure(
     const RefPtr<AllocationHandle>& aHandle,

--- a/dom/media/webrtc/MediaEngineRemoteVideoSource.cpp
+++ b/dom/media/webrtc/MediaEngineRemoteVideoSource.cpp
@@ -319,16 +319,20 @@ MediaEngineRemoteVideoSource::Start(cons
 }
 
 nsresult
 MediaEngineRemoteVideoSource::Stop(const RefPtr<const AllocationHandle>& aHandle)
 {
   LOG((__PRETTY_FUNCTION__));
   AssertIsOnOwningThread();
 
+  if (mState == kStopped || mState == kAllocated) {
+    return NS_OK;
+  }
+
   MOZ_ASSERT(mState == kStarted);
 
   if (camera::GetChildAndCall(&camera::CamerasChild::StopCapture,
                               mCapEngine, mCaptureIndex)) {
     MOZ_DIAGNOSTIC_ASSERT(false, "Stopping a started capture failed");
   }
 
   {

--- a/dom/media/webrtc/MediaEngineSource.h
+++ b/dom/media/webrtc/MediaEngineSource.h
@@ -166,16 +166,19 @@ public:
                                const char** aOutBadConstraint) = 0;
 
   /**
    * Called by MediaEngine to stop feeding data to the track associated with
    * the given AllocationHandle.
    *
    * If this was the last AllocationHandle that had been started,
    * the underlying device will be stopped.
+   *
+   * Double-stopping a given allocation handle is allowed and will return NS_OK.
+   * This is necessary sometimes during shutdown.
    */
   virtual nsresult Stop(const RefPtr<const AllocationHandle>& aHandle) = 0;
 
   /**
    * Called by MediaEngine to deallocate a handle to this source.
    *
    * If this was the last registered AllocationHandle, the underlying device
    * will be deallocated.

--- a/dom/media/webrtc/MediaEngineTabVideoSource.cpp
+++ b/dom/media/webrtc/MediaEngineTabVideoSource.cpp
@@ -397,16 +397,21 @@ MediaEngineTabVideoSource::Draw() {
   mImage = image;
   mImageSize = size;
 }
 
 nsresult
 MediaEngineTabVideoSource::Stop(const RefPtr<const AllocationHandle>& aHandle)
 {
   AssertIsOnOwningThread();
+
+  if (mState == kStopped || mState == kAllocated) {
+    return NS_OK;
+  }
+
   MOZ_ASSERT(mState == kStarted);
 
   // If mBlackedoutWindow is true, we may be running
   // despite mWindow == nullptr.
   if (!mWindow && !mBlackedoutWindow) {
     return NS_OK;
   }