What are you doing prior to Firefox crashing? Something related to audio, perhaps streaming?

Yes. It does seem to have something to do with Audio/video. The crashes happen with all kinds of websites (Amazon, LinkedIn, etc.) But, now that I think of it, it does seem to happen when there is audio or video playing on the website.

I don't know enough on the subject but your crash report seems to point to Windows Audio Session API (WASAPI causing your crash.

Perhaps some one more well versed in Windows can tell you what to try. I don't go into my Windows system too much anymore.

Sloppy instructions incoming. Can you right click your Audio icon in your taskbar and go to Playback Devices. Try changing your main audio device to use Windows DirectAudio. Sorry I couldn't be much more help.

Make sure to run Windows Update Checker.

Also, Perform a System File Check to fix corrupted system files

Win 7, 8, 10, Vista: https://support.microsoft.com/en-us/kb/929833 Win XP: https://www.microsoft.com/resources/documentation/windows/xp/all/proddocs/en-us/system_file_checker.mspx?mfr=true

Wiki - Windows 10 System File Check http://answers.microsoft.com/en-us/windows/wiki/windows_10-update/system-file-check-sfc-scan-and-repair-system-files/bc609315-da1f-4775-812c-695b60477a93

If there is still a problem, you could also ask here; https://support.microsoft.com http://answers.microsoft.com/en-US/windows/forum/windows_10