 <p>Your server delivers the resource <a href="http://dev.fristil.se/hbh/wp-content/themes/skal/images/video/bubblybeer.webm" rel="nofollow">http://dev.fristil.se/hbh/wp-content/themes/skal/images/video/bubblybeer.webm</a> with the HTTP header <code>Content-Type: text/plain</code> – and therefore Firefox refuses to treat it as anything else.</p> <p>“Teach” your server to deliver such content as <code>video/webm</code>.</p> <p>(Same goes for your ogv – your server also says that resource would be text, should be <code>video/ogg</code> instead.)</p>