Could you start Firefox in its Safe Mode. That's a standard diagnostic tool to bypass interference by extensions (and some custom settings). More info: Diagnose Firefox issues using Troubleshoot Mode.

You can start Firefox in Safe Mode by holding down the Shift key when starting Firefox.

In the small dialog that should appear, click "Start in Safe Mode" (not Reset)

Next, when Firefox crashes, it usually records information about what was happening at that moment. You can submit that data to Mozilla and share it with forum volunteers to see whether it points to the solution. Please check the support article "Firefox Crashes" (especially the last section) for steps to get those crash IDs, and then post some of the recent ones here.

If you cannot start Firefox at all even in Safe Mode, please check for these issues:

• Uninstall BitGuard to fix crashes with Firefox
• Troubleshoot Firefox issues caused by malware

Try to boot the computer in Windows Safe Mode with network support (press F8 on the boot screen) as a test to see if that helps.