Start Firefox in Safe Mode {web link} by holding down the <Shift> (Mac=Options) key, and then starting Firefox.

A small dialog should appear. Click Start In Safe Mode (not Refresh). Is the problem still there?

How to crash Firefox (All Systems); Instructions here; https://developer.mozilla.org/en-US/docs/Mozilla/How_to_report_a_hung_Firefox

This link has a program that can crash Firefox.

This is a new installation of Firefox due to complete reload of o/s Tried safe mode - same result firefox works but when I close it, I get the same message in reliability monitor. firefox crashed.

rmodine said

firefox works but when I close it, I get the same message in reliability monitor. firefox crashed.

Firefox sometimes does "hang" or freeze while shutting down, and if too much time passes, a watchdog process will terminate Firefox and trigger the Mozilla Crash Reporter dialog. Are you seeing that?

Or maybe Windows 10 has its own opinion about what is supposed to happen when Firefox shuts down?

If you usually close Firefox using the "X" button at the right end of the title bar, try using the Exit command instead. Either:

• "3-bar" menu button > "power" button
• (menu bar) File > Exit

That gives Firefox the best shot at an orderly shutdown. (In Firefox and many other Windows apps, you can reveal the classic menu bar by tapping the Alt key or the F10 function key.)

Nothing seems to help. This is a 64bit system but firefox says it is 32bit. is there a 64 bit version of firefox?

There is a 64-bit version of Firefox for 64-bit Windows. This article has more information on how to switch: How to switch from 32-bit to 64-bit Firefox.

I have installed the 64 bit version. So far, no new crashes. Calling it solved for now