I was looking at some bugs on bugzilla, when i noticed a OpenGL related bug. The moz devs said in that bug that AMD has yet to implement some "surface transform" in their Catalyst drivers. Without that, the OpenGL on AMD hardware would be very slow.webgl.prefer-native-gl true/false
default: false
You can tell the browser to use native OpenGL for WebGL 3D hardware accelerated graphics, instead of the ANGLE DirectX wrapper. This may be faster on some drivers/graphics cards, but can also cause rendering problems or system instability
So to all AMD card owners, do not enable OpenGL from the option given above.
I cant remember the bug no., will try to search it for reference.
Edit : they seem to have blacklisted AMD 12.8 drivers, as it has multiple issues, specially with crossfireX, custom profiles, and Flash. 12.9 beta fixes them.