NoScript's video blocking breaks Youtube html5
Using the latest tbb (0.2.2.33-3) for osx and linux on youtube, opt-in to the html5 video test, try to browse for html5 videos on youtube. Either none exist, or tbb html5 video support doesn't work.
Try this on vimeo, which automatically swaps between flash and html5 if the browser identification string implies support. Always get the flash video 'install flash'. message.
The only place I can get html5 video to work is on tor's own website.