- First thing to do: reset Firefox to it's defaults. See https://support.mozilla.org/en-US/kb/refresh-firefox-reset-add-ons-and-settings.
- Second thing to do: delete or rename the Firefox profile in your Appdata>Roaming and Appdata>Local folder, so it will start with a totally new one.
Did you check the Firefox crash reports, and are they being sent to Mozilla?
I reformated my computer on Feb. 24, just because. I do this about every 4 or 5 months just to keep my Dell Inspiron 3647‘desktop’ pc fresh. Everything seemed to be working great. No apparent issues. Then yesterday, I check the “view reliability history”. And I saw that “every” day, beginning on the 24th, there were these “Firefox stopped working”. I looked into Google, and it suggested that I do the following: download a fresh copy of FireFox, delete the C:\Program Folder for Mozilla, reboot, run register cleaner ( I have Ccleaner ), and then reinstall Firefox. Did this a couple of times. Still getting the same error message. Message is as follows:
Description
Faulting Application Path: C:\Program Files\Mozilla Firefox\firefox.exe
Problem signature
Problem Event Name: APPCRASH
Application Name: firefox.exe
Application Version: 58.0.2.6611
Application Timestamp: 5a7a193e
Fault Module Name: ntdll.dll
Fault Module Version: 10.0.16299.248
Fault Module Timestamp: effc9126
Exception Code: c0000005
Exception Offset: 0000000000020b2d
OS Version: 10.0.16299.2.0.0.768.101
Locale ID: 1033
Additional Information 1: cdff
Additional Information 2: cdffdb0086c785e65a5a9f7343ea6148
Additional Information 3: 85f7
Additional Information 4: 85f7c7774badc9cdc5ea2accd9c266fd
Extra information about the problem
Bucket ID: 233935c30f09c7710d3d9060066f2ae6 (2106998942778469094)
My computer seems to be working fine, I just keep getting these errors. Today I have 15 of these ‘critical events’. Needless to say all updates done, windows 10. I opened Internet Explorer, used it a little bit, and there were no “critical events”.
Thanks in advance for any suggestions.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic