Seeing this lock up on Debian Jessie when watching youtube HTML5 videos in
firefox.
kernel
Linux oberon 3.16-3-amd64 #1 SMP Debian 3.16.5-1 (2014-10-10) x86_64 GNU/Linux
Mesa 10.2.8-1
libdrm-radeon1 2.4.58-2
xserver-xorg-video-radeon 1:7.5.0-1
On a [AMD/ATI] Cape Verde PRO [Radeon HD 7750 / R7 250E]

I have logs which i can post, but it looks like you already have quite a few.