I have a problem with html5 videoplayer on youtube. It's freezeng randomly (mostly after pause) and video loosing sound. I using the newest version of firefox on windows 7 x64 bits. I am working on PC.
This is a strange behaviour. If your computer is recent enough, there mustn't be any problem on playing HTML5 videos on Youtube. If you like to continue with Firefox, try to use this extension. If not, try another browser, like Google Chrome