I was trying to take advantage of that new HTML5 <video> tag, and Firefox 3.5's native Ogg support, by embedding an .ogv video. Here is the references I used:
http://www.w3schools.com/tags/html5_video.asp
http://camendesign.com/code/video_for_everybody
You need to make sure you your web server is set-up with the correct MIME types. Otherwise, Firefox 3.5 will not show the video.
I found the following at http://camendesign.com/code/ and it worked for me. Add the following to your .htaccess file:
AddType video/ogg .ogv
AddType video/mp4 .mp4
AddType video/x-m4v .m4v
The Camen Design site has a good overview of using the <video> tag with a Flash fallback (for browsers that don't use the <video> tag). Hope that helps.
REFERENCES
http://www.linuxquestions.org/questions/programming-9/ogv-video-does-not-display-with-video-tag-in-firefox-3-5-a-737554/
http://blog.gingertech.net/2008/09/05/new-ogg-mime-types-ratified/