nwenzel, your video at http://blog.simplelegal.com/simplelegal-reports doesn't play on Firefox. I'd suggest using a service like Vimeo or one of the tools listed at http://praegnanz.de/html5video/ to make sure you have a Flash fallback.
Odd, video on the site works for me on Firefox (25.0.1 on OS X), and we're actually using mediaelement.js which is listed on the page you link to. What OS/version of Firefox are you using?
I checked into this further and it looks like a bad interaction with the FlashBlock plugin on Firefox. When I whitelisted the site, it worked fine.