Firefox plays default content SWFObject with Flash player ok

Hello,

I use SWFObject to define HTML 5 video content as a fallback to flash video, basically in line with the instructions given here:

http://gotoandlearn.com/play.php?id=128

code is:

<script type="text/javascript">

      swfobject.embedSWF("test.swf","player1","938","533","9");

</script>

<div id="player1">

<video src="video.mp4"

  controls="controls"

  autoplay="autoplay"

  autobuffer="autobuffer"

  height="533"

  width="938">

  </video>

</div>

This was a stable solution until very recently, when Firefox 21.0 started to play both the flash content AND the fallback video content. Chrome, IE etc are ok. Flash Player 11.7

Any ideas?

Thank you -

Jay