Ah, i see now. Youtube seems to have added a silly user-agent check since, and prevents from using HTML5 mode for the other browsers. Really stupid.

Just go to settings and spoof as safari then.

But in any case, the youtube.js script allows to play all of them by replacing flash with html5 builtin player. Current 1.8 version isn't totally complete regarding controls, but next version will be better: http://fabportnawak.free.fr/owbshots/builtin-mediaplayer-youtube-script.png

[ Edited by Fab on 2010/7/30 15:19 ]