Recently I've found one bug which in Debug build end with output: gfx/cairo/cairo/src/cairo.c:437: _moz_cairo_destroy: Assertion `((*&(&cr->ref_count)->ref_count) > 0)' failed. I've found reason of this abort, and found that context (SW) in Compositor thread destroyed by gfxContext DTOR in content thread. I guess in order to use cairo and OMTC we should remove this line http://hg.mozilla.org/mozilla-central/diff/5036a2b3fc8a/gfx/cairo/cairo/src/cairo-platform.h#l1.12 and add CAIRO_HAS_PTHREAD where it is possible.
Is this a dupe of bug 705691?
Sounds like it is.