--- a/dom/media/MediaDecoderReader.h
+++ b/dom/media/MediaDecoderReader.h
@@ -217,30 +217,16 @@ public:
   virtual MediaQueue<AudioData>& AudioQueue() { return mAudioQueue; }
   virtual MediaQueue<VideoData>& VideoQueue() { return mVideoQueue; }
 
   AbstractCanonical<media::TimeIntervals>* CanonicalBuffered()
   {
     return &mBuffered;
   }
 
-  void DispatchSetStartTime(int64_t aStartTime)
-  {
-    RefPtr<MediaDecoderReader> self = this;
-    nsCOMPtr<nsIRunnable> r =
-      NS_NewRunnableFunction([self, aStartTime] () -> void
-    {
-      MOZ_ASSERT(self->OnTaskQueue());
-      MOZ_ASSERT(!self->HaveStartTime());
-      self->mStartTime.emplace(aStartTime);
-      self->UpdateBuffered();
-    });
-    OwnerThread()->Dispatch(r.forget());
-  }
-
   TaskQueue* OwnerThread() const
   {
     return mTaskQueue;
   }
 
   // Returns true if the reader implements RequestAudioData()
   // and RequestVideoData() asynchronously, rather than using the
   // implementation in this class to adapt the old synchronous to
@@ -295,24 +281,16 @@ protected:
   //
   // The OggReader relies on this base implementation not performing I/O,
   // since in FirefoxOS we can't do I/O on the main thread, where this is
   // called.
   virtual media::TimeIntervals GetBuffered();
 
   RefPtr<MediaDataPromise> DecodeToFirstVideoData();
 
-  bool HaveStartTime()
-  {
-    MOZ_ASSERT(OnTaskQueue());
-    return mStartTime.isSome();
-  }
-
-  int64_t StartTime() { MOZ_ASSERT(HaveStartTime()); return mStartTime.ref(); }
-
   // Queue of audio frames. This queue is threadsafe, and is accessed from
   // the audio, decoder, state machine, and main threads.
   MediaQueue<AudioData> mAudioQueue;
 
   // Queue of video frames. This queue is threadsafe, and is accessed from
   // the decoder, state machine, and main threads.
   MediaQueue<VideoData> mVideoQueue;
 
@@ -340,28 +318,16 @@ protected:
   // Duration, mirrored from the state machine task queue.
   Mirror<media::NullableTimeUnit> mDuration;
 
   // Whether we should accept media that we know we can't play
   // directly, because they have a number of channel higher than
   // what we support.
   bool mIgnoreAudioOutputFormat;
 
-  // The start time of the media, in microseconds. This is the presentation
-  // time of the first frame decoded from the media. This is initialized to -1,
-  // and then set to a value >= by MediaDecoderStateMachine::SetStartTime(),
-  // after which point it never changes (though SetStartTime may be called
-  // multiple times with the same value).
-  //
-  // This is an ugly breach of abstractions - it's currently necessary for the
-  // readers to return the correct value of GetBuffered. We should refactor
-  // things such that all GetBuffered calls go through the MDSM, which would
-  // offset the range accordingly.
-  Maybe<int64_t> mStartTime;
-
   // This is a quick-and-dirty way for DecodeAudioData implementations to
   // communicate the presence of a decoding error to RequestAudioData. We should
   // replace this with a promise-y mechanism as we make this stuff properly
   // async.
   bool mHitAudioDecodeError;
   bool mShutdown;
 
   // Used to send TimedMetadata to the listener.

--- a/dom/media/MediaDecoderReaderWrapper.cpp
+++ b/dom/media/MediaDecoderReaderWrapper.cpp
@@ -224,20 +224,16 @@ MediaDecoderReaderWrapper::OnMetadataRea
 {
   MOZ_ASSERT(mOwnerThread->IsCurrentThreadIn());
   if (mShutdown) {
     return;
   }
 
   if (mStartTime.isNothing()) {
     mStartTime.emplace(aMetadata->mInfo.mStartTime);
-    // Note: MFR should be able to setup its start time by itself without going
-    // through here. MediaDecoderReader::DispatchSetStartTime() will be removed
-    // once we remove all the legacy readers' code in the following bugs.
-    mReader->DispatchSetStartTime(StartTime().ToMicroseconds());
   }
 }
 
 void
 MediaDecoderReaderWrapper::SetVideoBlankDecode(bool aIsBlankDecode)
 {
   MOZ_ASSERT(mOwnerThread->IsCurrentThreadIn());
   nsCOMPtr<nsIRunnable> r =