Firefox 34 on Linux crashing constantly, with AMD GPU + Proprietary driver

Question

Firefox 34 is constantly crashing, at random intervals. Sometimes the crash occurs as soon as the browser starts, sometimes it'll be fine for a couple of minutes, sometimes it's an hour.
I am using an AMD GPU with the proprietary driver on Linux.
Flash is disabled.
What I have tried:
Disabling hardware acceleration
Disabling all add-ons
Creating a new profile
Re-downloading the package
Crash signature: https://crash-stats.mozilla.com/report/list?product=Firefox&signature=libc-2.19.so%400x94470
The issue started in version 32-33, I don't remember which.
I don't know if it's related, but HTML5 x.264/MP4 playback has stopped working as well. Now I am only able to play webm video.
The crashes seem to happen more frequently when browsing YouTube.

Answer 1

In the address bar, type '''about:crashes'''<enter>.''' Note:''' If any reports do not
have '''BP''' in front of the numbers, click it and select '''Submit'''.
Using your mouse, '''mark''' the most '''resent 7 - 10''' crash reports, and
'''copy''' them. Now go to the reply box below and '''paste''' them in.
'''[https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode Start Firefox in Safe Mode]''' {web link}
While you are in safe mode;
Type '''about:preferences#advanced'''<Enter> in the address bar.
Under '''Advanced,''' Select '''General.'''
Look for and turn off '''Use Hardware Acceleration'''.
Poke around safe web sites. Are there any problems?