Dear Maintainer,

Youtube now defaults to the HTML5 player on Firefox Aurora.
With this player, I get really bad performances on IceWeasel 36.0a2. The video
is not smooth at all and it it makes the whole tab lag, especially when I mouse
my mouse over the video.

I can reproduce in safe mode.
I can't reproduce with upstream builds (Firefox Developer Edition 36.0a2).

Regards,