I installed this on my WP 3.1.2 and had problems with video from the start.
Firefox 3.5.? was a grey box, but IE showed a small version albeit without the fullscreen, duration, volume etc.
Upgraded to FF 4.0.1, but still the same grey box.
I eventually tracked it down to WP Minify.
To make it work together, you need to go to Settings | WP Minify
Now it work fine :)