If Video Alpha is playing a YouTube video in Firefox in HTML5 mode, then when switching to speed 1.0 it will simply reload the iframe, instead of using the built-in method to change the speed. The fixes the bug temporarily, while the YouTube team fixes the bug internally in the API. Commented additions to fix YouTube firefox speed 1.0 switch bug.

common/lib/xmodule/xmodule/js/src/videoalpha/display/video_player.coffee

@@ -66,7 +66,16 @@ class @VideoPlayerAlpha extends SubviewAlpha
     if @video.end
       # work in AS3, not HMLT5. but iframe use AS3
       @playerVars.end = @video.end
+
+    # There is a bug which prevents YouTube API to correctly set the speed to 1.0 from another speed
+    # in Firefox when in HTML5 mode. There is a fix which basically reloads the video at speed 1.0
+    # when this change is requested (instead of simply requesting a speed change to 1.0). This has to
+    # be done only when the video is being watched in Firefox. We need to figure out what browser is
+    # currently executing this code.
+    @video.isFirefox = navigator.userAgent.toLowerCase().indexOf('firefox') > -1
+
     if @video.videoType is 'html5'
+      @video.playerType = 'browser'
       @player = new HTML5Video.Player @video.el,
         playerVars: @playerVars,
         videoSources: @video.html5Sources,
@@ -79,6 +88,7 @@ class @VideoPlayerAlpha extends SubviewAlpha
         youTubeId = @video.videos['1.0']
       else
         youTubeId = @video.youtubeId()
+      @video.playerType = 'youtube'
       @player = new YT.Player @video.id,
         playerVars: @playerVars
         videoId: youTubeId
@@ -235,13 +245,18 @@ class @VideoPlayerAlpha extends SubviewAlpha
     if @video.videoType is 'youtube'
       if @video.show_captions is true
         @caption.currentSpeed = newSpeed
-    if @video.videoType is 'html5'
-      @player.setPlaybackRate newSpeed
-    else if @video.videoType is 'youtube'
+
+    # We request the reloading of the video in the case when YouTube is in Flash player mode,
+    # or when we are in Firefox, and the new speed is 1.0. The second case is necessary to
+    # avoid the bug where in Firefox speed switching to 1.0 in HTML5 player mode is handled
+    # incorrectly by YouTube API.
+    if (@video.videoType is 'youtube') or ((@video.isFirefox) and (@video.playerType is 'youtube') and (newSpeed is '1.0'))
       if @isPlaying()
         @player.loadVideoById(@video.youtubeId(), @currentTime)
       else
         @player.cueVideoById(@video.youtubeId(), @currentTime)
+    else if @video.videoType is 'html5'
+      @player.setPlaybackRate newSpeed
     if @video.videoType is 'youtube'
       @updatePlayTime @currentTime