Is it using HTML5 on YouTube itself, or the Flash Player?
Hmm, this is weird. I am not sure if its html5 or flash because formerly I used to be able to click on settings or right click and get some clue something about flash or html5 player, Now there is no such thing. So I am not sure
I use a css file to stop the YouTube subscriptions list on the left hand side showing, which slowed YouTube down horribly on Opera 12, but I don't use any specific user js that does anything related to YouTube. The YouTube Center extension is the only thing that I use.
So what happens if you right click on a playing YouTube video?
Nothing happens when I right click nothing happens. Do you have the oex file for the youtube center? I was gonna try it long time ago but something went wrong and I gave up on the link I had
The latest version of YouTube Center is here.
Give it a try, but I don't know if it will solve your problem.
It can no longer force the use of the Flash Player IIRC as YouTube removed that option.