MediaElement.js in Firefox 4 Beta 10?

I know I'm probably just going something wrong, but I can't figure it out why my MediaElement.js videos aren't playing in Firefox 4 Beta 10. They're working fine in Firefox 3.6.13. So far, I've only tested this in Mac OS 10.6.6.

http://www.nolanfans.com/trailers

I think the problem is that cl.ly is send the content-type of the .webm file as "binary/octet-stream" but Firefox (and Opera) requires it to be "video/webm". I don't know if you can get cl.ly to change that, but for now you could just remove the webm file and Firefox 4 would play the MP4 via flash just like Firefox 3 does.