Thanks! I'll have to do some more work on getting it to work right on Firefox. It is a little different since FF doesn't have native h.264 support so it goes to a Flash fallback. I wanted to make it easy, so that you would just have one source video, rather than do the .ogg/.webm cascade. So...I'll have to work a little more on getting the flash fallback player to scale better/faster.
Running Nightly (Firefox alphas) and it works here. The fallback to Flash explains why it's so laggy here on OS X though, making it a distraction rather than a positive addition to the site.
Still, I like the idea behind it and I hope these things can be solved in later versions.
[update]: this is amazing great work!
[update]: here is a screenshot: http://i.imgur.com/Mogn3.png hopefully having the firebug inspector open helps...