What if you install gstreamer0.10-ffmpeg via apt and then open up Abrowser,
type about:config, search for media.gstreamer.enabled and set to true.
You may have to restart the browser and go to https://www.youtube.com/html5
or http://beta.html5test.com to see if it worked.
What also works for me if YouTube forces Flash is to get a user agent
switcher extension and once on YouTube, set your user agent to iPad with iOS
7 to force H.264. I know that H.264 is patented and all, but if there is no
WebM stream you either have Flash or H.264.
