Comment 10 for bug 1314924

As I reported upstream (mozilla-bugs:1005501), the bug is due to xserver-xorg-video-intel, and was fixed somewhere between 2:2.99.910 and 2:2.99.911 (c.f. freedesktop:79165).
The bug is therefore already fixed in 14.10, so it should be fixed in 14.04 once the 14.04.2 point release is published (i.e. "xserver-xorg-video-intel-lts-utopic" becomes available on trusty-updates) on 5 February 2015. I don't see a 12.04.6 point release scheduled, however, so if 12.04.5 is affected, upgrading to 14.04.2 may be necessary.
Aside from using ppa:xorg-edgers/ppa (dangerous) and xserver-xorg-video-intel-lts-utopic on ppa:canonical-x/x-staging (which doesn't look meant for general or even troubleshooting use), I otherwise don't know how to obtain a packaged fix ahead of time for 14.04 or at all for 12.04. Maybe someone at Ubuntu-X can help.