Only browser I got your app working in was Chrome. What browser were you primarily testing the application in? What version? Because Firefox just released an update this morning and it could very well be the culprit.
I not only could not get Firefox (3.5.5), IE7, or Safari to work with your HTML5 YouTube app, but I could not get YouTube's app to work either; I hope this fact mitigates your worries.
Well I'm not gonna blame you for it not working in Firefox. I've actually had to re-write client-side code (generally just quick hacks, similar to your project) solely for Firefox patching some sort of quirk or behavior change into their browser. It can get especially annoying if you're always testing with the most recent version.
I not only could not get Firefox (3.5.5), IE7, or Safari to work with your HTML5 YouTube app, but I could not get YouTube's app to work either; I hope this fact mitigates your worries.