Flash causes behind the crash which can be solved by some tricks such as

• Using Flash Block add-on from about:addons (tyoe into url and search that one).
• Change settings from Always Active to Never Active again in add-ons> plug-in section.
• paste crash report id from about:crashes(type in url and copy the id which startes from bp-xxxx-)

PS: did you find any pattern like it hangs/crashes on particular site/video etc.

You can check for problems with current Shockwave Flash plugin versions and try this:

• check for updates for your graphics drive drivers
  https://support.mozilla.org/kb/upgrade-graphics-drivers-use-hardware-acceleration
• disable protected mode in the Flash plugin (Flash 11.3+ on Windows Vista and later)
• disable hardware acceleration in the Flash plugin

See also:

• http://kb.mozillazine.org/Flash#Troubleshooting

If you have submitted crash reports then please post the IDs of one or more recent crash reports that have a "bp-" prefix:

• bp-xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx

You can find the Report ID of recent crash reports on the "Help > Troubleshooting Information" page (about:support).

• Click the "All Crash Reports" button on this page to open the about:crashes page and see all crash reports.

If necessary then you can open about: pages via the location/address bar.

See:

• http://kb.mozillazine.org/Mozilla_Crash_Reporter
• https://support.mozilla.org/kb/Mozilla+Crash+Reporter