--- a/dom/media/MediaDecoderStateMachine.cpp
+++ b/dom/media/MediaDecoderStateMachine.cpp
@@ -423,32 +423,53 @@ public:
   State GetState() const override
   {
     return DECODER_STATE_DECODING_FIRSTFRAME;
   }
 
   bool HandleAudioDecoded(MediaData* aAudio) override
   {
     mMaster->Push(aAudio, MediaData::AUDIO_DATA);
-    mMaster->MaybeFinishDecodeFirstFrame();
+    MaybeFinishDecodeFirstFrame();
     return true;
   }
 
   bool HandleVideoDecoded(MediaData* aVideo, TimeStamp aDecodeStart) override
   {
     mMaster->Push(aVideo, MediaData::VIDEO_DATA);
-    mMaster->MaybeFinishDecodeFirstFrame();
+    MaybeFinishDecodeFirstFrame();
     return true;
   }
 
   bool HandleEndOfStream() override
   {
-    mMaster->MaybeFinishDecodeFirstFrame();
+    MaybeFinishDecodeFirstFrame();
     return true;
   }
+
+private:
+  // Notify FirstFrameLoaded if having decoded first frames and
+  // transition to SEEKING if there is any pending seek, or DECODING otherwise.
+  void MaybeFinishDecodeFirstFrame()
+  {
+    MOZ_ASSERT(!mMaster->mSentFirstFrameLoadedEvent);
+
+    if ((mMaster->IsAudioDecoding() && mMaster->AudioQueue().GetSize() == 0) ||
+        (mMaster->IsVideoDecoding() && mMaster->VideoQueue().GetSize() == 0)) {
+      return;
+    }
+
+    mMaster->FinishDecodeFirstFrame();
+
+    if (mMaster->mQueuedSeek.Exists()) {
+      mMaster->InitiateSeek(Move(mMaster->mQueuedSeek));
+    } else {
+      SetState(DECODER_STATE_DECODING);
+    }
+  }
 };
 
 class MediaDecoderStateMachine::DecodingState
   : public MediaDecoderStateMachine::StateObject
 {
 public:
   explicit DecodingState(Master* aPtr) : StateObject(aPtr) {}
 
@@ -1245,36 +1266,16 @@ MediaDecoderStateMachine::OnNotDecoded(M
   }
 
   MaybeStopPrerolling();
 
   mStateObj->HandleEndOfStream();
 }
 
 void
-MediaDecoderStateMachine::MaybeFinishDecodeFirstFrame()
-{
-  MOZ_ASSERT(OnTaskQueue());
-  MOZ_ASSERT(!mSentFirstFrameLoadedEvent);
-
-  if ((IsAudioDecoding() && AudioQueue().GetSize() == 0) ||
-      (IsVideoDecoding() && VideoQueue().GetSize() == 0)) {
-    return;
-  }
-
-  FinishDecodeFirstFrame();
-
-  if (mQueuedSeek.Exists()) {
-    InitiateSeek(Move(mQueuedSeek));
-  } else {
-    SetState(DECODER_STATE_DECODING);
-  }
-}
-
-void
 MediaDecoderStateMachine::OnVideoDecoded(MediaData* aVideo,
                                          TimeStamp aDecodeStartTime)
 {
   MOZ_ASSERT(OnTaskQueue());
   MOZ_ASSERT(aVideo);
 
   // Handle abnormal or negative timestamps.
   mDecodedVideoEndTime = std::max(mDecodedVideoEndTime, aVideo->GetEndTime());

--- a/dom/media/MediaDecoderStateMachine.h
+++ b/dom/media/MediaDecoderStateMachine.h
@@ -528,20 +528,16 @@ protected:
   // decoded and playable. This is the sum of the number of usecs of audio which
   // is decoded and in the reader's audio queue, and the usecs of unplayed audio
   // which has been pushed to the audio hardware for playback. Note that after
   // calling this, the audio hardware may play some of the audio pushed to
   // hardware, so this can only be used as a upper bound. The decoder monitor
   // must be held when calling this. Called on the decode thread.
   int64_t GetDecodedAudioDuration();
 
-  // Notify FirstFrameLoaded if having decoded first frames and
-  // transition to SEEKING if there is any pending seek, or DECODING otherwise.
-  void MaybeFinishDecodeFirstFrame();
-
   void FinishDecodeFirstFrame();
 
   // Completes the seek operation, moves onto the next appropriate state.
   void SeekCompleted();
 
   // Queries our state to see whether the decode has finished for all streams.
   bool CheckIfDecodeComplete();