Qualcuno mi aiuta a capire perchè questa cosa?

Codice PHP:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Untitled Document</title>
</head>

<body>

<video id="video1" width="640" height="360" autoplay loop >
   <source src="your-v.webm" type="video/webm" />
</video>

    

<video id="video2" width="640" height="360" autoplay loop >

    <source src="http://videos-cdn.mozilla.net/serv/marketing/firefox4/FF4_Jess3Features_VO_1.webm" type="video/webm" />
</video>

</body>
</html> 
In Chrome funzionano tutti e DUE (sono lo stesso file e filmato ma con nomi diversi), mentre in FireFox NO?????????????????????

Grazie