--- a/dom/media/MediaStreamGraph.cpp
+++ b/dom/media/MediaStreamGraph.cpp
@@ -1019,17 +1019,17 @@ MediaStreamGraphImpl::OpenAudioInput(int
     mAbstractMainThread->Dispatch(runnable.forget());
     return NS_OK;
   }
   class Message : public ControlMessage {
   public:
     Message(MediaStreamGraphImpl *aGraph, int aID,
             AudioDataListener *aListener) :
       ControlMessage(nullptr), mGraph(aGraph), mID(aID), mListener(aListener) {}
-    virtual void Run()
+    void Run() override
     {
       mGraph->OpenAudioInputImpl(mID, mListener);
     }
     MediaStreamGraphImpl *mGraph;
     int mID;
     RefPtr<AudioDataListener> mListener;
   };
   // XXX Check not destroyed!
@@ -1090,17 +1090,17 @@ MediaStreamGraphImpl::CloseAudioInput(Au
                    RefPtr<AudioDataListener>(aListener));
     mAbstractMainThread->Dispatch(runnable.forget());
     return;
   }
   class Message : public ControlMessage {
   public:
     Message(MediaStreamGraphImpl *aGraph, AudioDataListener *aListener) :
       ControlMessage(nullptr), mGraph(aGraph), mListener(aListener) {}
-    virtual void Run()
+    void Run() override
     {
       mGraph->CloseAudioInputImpl(mListener);
     }
     MediaStreamGraphImpl *mGraph;
     RefPtr<AudioDataListener> mListener;
   };
   this->AppendMessage(MakeUnique<Message>(this, aListener));
 }
@@ -2438,17 +2438,17 @@ void
 MediaStream::AddTrackListener(MediaStreamTrackListener* aListener,
                               TrackID aTrackID)
 {
   class Message : public ControlMessage {
   public:
     Message(MediaStream* aStream, MediaStreamTrackListener* aListener,
             TrackID aTrackID) :
       ControlMessage(aStream), mListener(aListener), mTrackID(aTrackID) {}
-    virtual void Run()
+    void Run() override
     {
       mStream->AddTrackListenerImpl(mListener.forget(), mTrackID);
     }
     RefPtr<MediaStreamTrackListener> mListener;
     TrackID mTrackID;
   };
   GraphImpl()->AppendMessage(MakeUnique<Message>(this, aListener, aTrackID));
 }
@@ -2471,17 +2471,17 @@ void
 MediaStream::RemoveTrackListener(MediaStreamTrackListener* aListener,
                                  TrackID aTrackID)
 {
   class Message : public ControlMessage {
   public:
     Message(MediaStream* aStream, MediaStreamTrackListener* aListener,
             TrackID aTrackID) :
       ControlMessage(aStream), mListener(aListener), mTrackID(aTrackID) {}
-    virtual void Run()
+    void Run() override
     {
       mStream->RemoveTrackListenerImpl(mListener, mTrackID);
     }
     RefPtr<MediaStreamTrackListener> mListener;
     TrackID mTrackID;
   };
   GraphImpl()->AppendMessage(MakeUnique<Message>(this, aListener, aTrackID));
 }
@@ -2500,17 +2500,17 @@ void
 MediaStream::AddDirectTrackListener(DirectMediaStreamTrackListener* aListener,
                                     TrackID aTrackID)
 {
   class Message : public ControlMessage {
   public:
     Message(MediaStream* aStream, DirectMediaStreamTrackListener* aListener,
             TrackID aTrackID) :
       ControlMessage(aStream), mListener(aListener), mTrackID(aTrackID) {}
-    virtual void Run()
+    void Run() override
     {
       mStream->AddDirectTrackListenerImpl(mListener.forget(), mTrackID);
     }
     RefPtr<DirectMediaStreamTrackListener> mListener;
     TrackID mTrackID;
   };
   GraphImpl()->AppendMessage(MakeUnique<Message>(this, aListener, aTrackID));
 }
@@ -2527,17 +2527,17 @@ void
 MediaStream::RemoveDirectTrackListener(DirectMediaStreamTrackListener* aListener,
                                        TrackID aTrackID)
 {
   class Message : public ControlMessage {
   public:
     Message(MediaStream* aStream, DirectMediaStreamTrackListener* aListener,
             TrackID aTrackID) :
       ControlMessage(aStream), mListener(aListener), mTrackID(aTrackID) {}
-    virtual void Run()
+    void Run() override
     {
       mStream->RemoveDirectTrackListenerImpl(mListener, mTrackID);
     }
     RefPtr<DirectMediaStreamTrackListener> mListener;
     TrackID mTrackID;
   };
   GraphImpl()->AppendMessage(MakeUnique<Message>(this, aListener, aTrackID));
 }