Hello kentmi, I noticed some other users recently with a similar problem which was caused by adware/malware. Here are a couple of tools which might help: Malwarebytes AdwCleaner and Norton Power Eraser

(Be sure to have Firefox closed when running scans)

Thanks, but did not work. I ran the Malwarebytes tool and while it found some PUPS, it did not solve the problem. I tried opening FF with same result. I approved changes, and my computer slows to basic lock up. Win 10 task manager (via Ctrl Alt Del) will not function either once I give permission and I have to shut down with power button.

Hi kentmi, Did you try Firefox in Safe Mode by press & hold the shift key while you launch?

Yes, with the same result. Command prompt "firefox.exe -p" failed as well.

You might want to consider backing up your profile and doing a clean install. Back up and restore information in Firefox profiles

Firefox keeps crashing at startup

Thanks, My_Cheese_Is_Slippin, I appreciate your time and expertise. I've found my profile and copied to desktop. I understand my profile will not be deleted by a clean install and unless I delete it and this the problem can persist. Should I delete it and then restore it after a clean install?

Hi kentmi. Don't delete the copy of your profile.

After you do a clean install, don't Restore your profile until you are convinced that Firefox is working properly.

If it is, then there is a problem in your profile. You can select files from your profile to restore like Bookmarks & Passwords, but I would re-check add-ons for possible malicious content.

Got it. But should I delete my profile from C:\AppData\Roaming\Mozilla\Firefox\Profiles? Uninstall does not delete this. Thanks

Hi kentmi, I would. There is also another part of your profile in C:\AppData\Local\Mozilla\Firefox\Profiles I would delete that one , also.

Back up and running. I think good to go. Can I just copy and paste bookmarkbackups folder from old profile? Or just the last file in the folder? I did not copy C:\AppData\Local\Mozilla\Firefox\Profiles. Don't think this should matter.

Thanks so much for your patient assistance!

Glad to hear it! Don't worry about the \Local\ folder. You should be able to copy the entire contents of the desktop folder to the C:\AppData\Roaming\Mozilla\Firefox\Profiles folder.