I've noticed that Youtube videos get embedded into the module by using both <object> and <embed> tags. This is a violation of XHTML 1.1 standards, because there exists no embed tag in XHTML 1.1 standard.
You should use the following to embed Youtube videos (and any other flashcontent as well):
<object width="390" height="320" type="application/x-shockwave-flash" data="http://www.youtube.com/v/HOB2PMrg67Q&rel=1&autoplay=0">
<param name="movie" value="http://www.youtube.com/v/HOB2PMrg67Q&rel=1&autoplay=0"/ >
<param name="wmode" value="transparent"/ >
</object>
This method works in Firefox (and all Gecko based browsers) and Internet Explorer. I'm not sure about Opera though.
Anyway: Using this method, the page validates correctly and the videos are working in all browsers.
See this page for more info:
http://alistapa…les/flashsatay