Comment # 18 on bug 20341 from Jason Detring

Created attachment 84576 [details]
firefox corruption

Setting vram_pushbuf=1 seems to help a little.  There are no more lockups, but
graphics get trashed when things start moving fast (x11perf) or big and
complicated (fullscreen web browsers).  Basically, any large volume data
transfers.

After the initial corruption occurs due to the mystery trigger, the system
never really goes back to normal.  There's broken graphics everywhere, even on
unrelated, small, sparsely-updated windows.

Things look roughly like I remember writing about in Comment #4, so this
parameter is probably doing the same job as 'CBLocation'.