User Agent: Mozilla/5.0 (Windows NT 6.2; WOW64) AppleWebKit/537.31 (KHTML, like Gecko) Chrome/26.0.1410.43 Safari/537.31 Steps to reproduce: <audio controls> <source src="song.mp3" type="audio/mpeg"> Your browser does not support the audio tag. </audio> <video width="320" height="240" controls> <source src="movie.mp4" type="video/mp4"> Your browser does not support the video tag. </video> Actual results: For the above code segment, i get the audio bar and the video player but the play button on the audio bar results in nothing. For the video, the video should be playing but the error says "No Video with Supported Format or MIME type found" Expected results: The audio and video should have played correctly.

For Firefox versions below 20 you currently need to add extra <source> tags for non-patented encoded versions of the audio and video, see https://developer.mozilla.org/en-US/docs/HTML/Supported_media_formats#WebM In Firefox 20 only Windows OS with the Windows Media Foundation is currently supported, see bug 799315