Firefox 3.6 doesn't support WebM video format. To view HTML5 WebM videos you need to download a nightly build of Firefox 4
For Ogv take care of frame rates and don't expect to show HD video. With a higher rate Firefox couldn't show my video, but when I reduce the frame rate and the quality, it works fine.
On which browser? IE for example doesn't support the video element at all. Also, the course element is a void element and as such shouldn't have an end tag. I've also noticed a bug in Firefox where the Ogg file has to be the first resource otherwise it doesn't work. This may have been fixed in 3.6.3 though.
My guess is that this is a duplicate of an earlier question. If so, the answer is: Make sure your server config has the following associations: