Windows Home or Pro version? If pro, try this tool to see if you have the same issue. https://www.howtogeek.com/399290/how-to-use-windows-10s-new-sandbox-to-safely-test-apps/

Do you have the same issue with Firefox in Safe Mode?

Besides Windows Defender, what security software are you running?

I am using windows 10 Home

The crash happened in Safe Mode to.

And I am not running any extra security software that I am aware of.

That said every time I run check for updates in Windows it downloads and reinstalls this:

Security Intelligence Update for Microsoft Defender Antivirus - KB2267602 (Version 1.401.1565.0) - Current Channel (Broad)

Then It says up to date, but if I restart my system it repeats again.

How about under a different user account? Where did you get Firefox from? Try a different version and make sure to install in a different directory than your current install. https://www.mozilla.org/en-US/firefox/channel/desktop/?reason=manual-update#nightly

Did you transfer data from the old PC to the new device ?

You can create a new profile as a quick test to see if your current profile is causing the problem.

See "Creating a profile":

• https://support.mozilla.org/en-US/kb/profile-manager-create-remove-switch-firefox-profiles

If the new profile works, you can transfer files from a previously used profile to the new profile, but be cautious not to copy corrupted files to avoid carrying over problems.

• https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile

I transferred Firefox from my C drive to another one. I am guessing the program files in C drive needed some kind of permission too read from which my Firefox did not give/get.