Given that it's happening with both Firefox AND Chrome, my usual "try this" for Firefox won't apply, but for anyone else: when debugging Firefox problems, first try disabling add-ons, and if that doesn't fix it, back up your profile directory and try running clean. Almost every Firefox-specific crash I've seen has involved either (A) a bad add-on, or (B) something else corrupted in the profile.

Since it's happening in both Chrome and newer versions Firefox, it could be a matter of GPU acceleration being bad, or a bad video drivers... you can try starting Chrome with the command line option " --disable-accelerated-compositing" or try some of these instructions:
http://www.howtogeek.com/howto/36918...heres-the-fix/
https://support.mozilla.org/en-US/questions/922995