Videos aren't playing in Firefox/Flash, don't know why. I'm working on it. For now use a browser that supports H.264 like Chrome, IE9, or Safari.
EDIT: And I still don't know why. It seems to be due to an anomaly in the way Flash gets the URL of the video file... and probably has something to do with its cache and enabling Clean URLs, because simple HTML5 in IE9 works just fine whatever I do.