Hi Samuel,
I was taking a look at your demo today in Firefox and found that it did not play anything. Chrome seemed to work ok.
Not sure why... I see wmode:'window' is missing, but that was only for older 3.6 Firefox support.
Just letting you know Firefox seems to have an issue.
Did you get to the bottom of your problem?
I suspect it could be encoding of the media... And Safari andChrome may use web-kit, but they are pretty different. Safari relies on QuickTime to play HTML5 media. Just uninstall QuickTime and you will find Safari is no longer HTML5 media.