Firefox excessive cpu usage with video content

[T. Taner]

Hi,

I'm on 10.3-Beta2 and have installed FF 44.0.2 via pkg. Cpu hits beyond
100% when watching online videos including youtube.  I have 8 core
i7-3630QM cpu and it very unusual to have such high load even when using
software decoding. For an instance, mpv barely hits beyond 10% with
software decoding and bare x11 output.

This is corresponding bug report at upstream:
https://bugzilla.mozilla.org/show_bug.cgi?id=1163327

html5 video testing: http://www.quirksmode.org/html5/tests/video.html

Regards
Taner.