Firefox won't start after updating Win 10 Pro to version 20H2  

I updated Win 10 Pro to version 20H2 and now Firefox will not start. No error message; no appearance in Task Manager. Here's what I've tried to no avail:

1) Uninstalled and reinstalled Firefox several times, including manually removing all remaining Firefox files (including my profile folder) after uninstall.

2) Tried to start Firefox with administrative privileges.

3) Clean booted Windows and tried to start.

4) Turned off Windows Firewall and tried to start.

5) Tried to start in Windows Safe Mode.

6) Firefox will start and run normally when installed into a Windows Sandbox on the same computer that won't start Firefox in Win 10 version 20H2.

7) Extensive Google searches to try to find a solution.

Oddly, Microsoft Edge will not start either, but Chrome starts and works normally.

- - - Updated - - -

It turned out that the 64-bit version of Firefox, which was downloading by default from Mozilla, won't run in my 64-bit Win 10 version 20H2, but the 32-bit version of Firefox runs. I occasionally had that kind of problem YEARS AGO with certain software, including Microsoft's own Office programs. Sad that this is still happening in 2021. This kind of annoyance is why Bill Gates probably uses Macs.

what version of Firefox were you using?
also do you have any 3rd party antivirus or internet security programs (aka. Norton, Mcafee, Kaspersky, etc.) installed on your machine?

Firefox 87.0. No antivirus programs other than Windows Security.

I saw this similar topic in another forum
perhaps post there & maybe someone there can help you

Thanks for the link! I subsequently had a number of other problems with 20H2, so I rolled the computer back to 1909 before the 10-day rollback period ended. I’ll try again with 21H1.

GatesUsesAMac said:

Thanks for the link! I subsequently had a number of other problems with 20H2, so I rolled the computer back to 1909 before the 10-day rollback period ended. I’ll try again with 21H1.

Strange ! I actually had same problem with Chrome and Edge after update. Did a clean reinstall for that and other reasons and all is well.