Firefox: youtube video freezes in full screen, how to fix it?

Question

Browsers

Firefox is slow, but not chrome. Tried to change different plugins, both about flash and about HTML5, there are no improvements.
Maybe it's the video card, I have a Radeon X1300. And so the percentage does not load, there is no heating ...
Firefox v.45
Google Chrome v.49.0.2623.108 (64-bit)
Ubuntu 14.04
I tried to completely reset the browser.
I've tried disabling/enabling hardware acceleration in the browser.
I sin on an old video card, radeon x1300.

Answer 1

This option helped: forum.ubuntu.ru/index.php?topic=275791.msg2179909#...

Answer 2

I also think that the old Radeon is to blame. Also under Ubuntu Chromium is faster (don't use Chrome on Linux). So just open the video in this browser.
Hardware acceleration can be done like this . Personally, after downgrading to an old video card, it stopped working for me.