Hi chris.mowat, This could be caused by a malware infection on your computer or it could be caused by an add-on that you have installed.

You can try these free programs to scan for malware, which will work with your existing antivirus software:

Microsoft Safety Scanner https://docs.microsoft.com/en-us/windows/security/ threat-protection/intelligence/safety-scanner-download

MalwareBytes Anti-Malware https://www.malwarebytes.com/premium/

Anti-Rootkit Utility - TDSSKiller https://www.bleepingcomputer.com/download/tdsskiller/

MalwareBytes AdwCleaner https://www.malwarebytes.com/adwcleaner/

ESET Online Scanner https://www.eset.com/us/home/online-scanner/

(Malwarebytes Chameleon - allows installation of Malwarebytes on an infected system https://www.malwarebytes.com/chameleon/)

Running more than one or all of the above mentioned Scan Tools is recommended since they scan at different levels of your computer. And, of course, run the scans with Firefox Closed.

There are also extensions available to help protect against malware, such as:

Malwarebytes Browser Guard https://addons.mozilla.org/en-US/firefox/addon/malwarebytes/

Further information can be found in the Troubleshoot Firefox issues caused by malware article: https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-caused-malware ___________________________________________________________________

If that doesn't fix the issue, try running Firefox in it's Safe Mode: https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode to see if the issue goes away. If it does, it's likely caused by an add-on, so you will need to use trial and error to determine the culprit.

Safe Mode will temporarily disable your extensions and themes, turn off hardware acceleration and reset toolbar and button customizations. When you leave Safe Mode and start Firefox up normally, your extensions, themes, and settings will return to the state they were in before you entered Safe Mode.

With Firefox open: select Menu select Help select Restart With Add-ons Disabled on the dialog select Restart on the next dialog select Start In Safe Mode (Do Not select Refresh)

With Firefox closed: press and hold the Shift (in Mac: Option) key launch Firefox on the dialog select Start In Safe Mode (Do Not select Refresh) ______________________________________________________

To quit Safe Mode: select Menu select Help select Restart With Add-ons Enabled

Or, Exit Firefox.

I also notice that you have a study running: Cookie Restrictions Strict List Study 2.1

You can Remove it if you think that it's causing the issue: About Studies https://support.mozilla.org/en-US/kb/shield

I followed your instructions to eliminate the "studies" only to find that I have in fact, NO STUDIES checked. So I'm not sure what the "Cookie Restrictions Strict List Study 2.1" is all about. I don't see that anywhere either.

In the meantime, I seem to have resolved the Firefox issue for now. But whatever changed, really damaged my boot record so now I'm dealing with that. It is NOT a virus. That much I know.

I've looked everywhere for some information on the "Cookie Restrictions" study and can't find anything. I came across another user who had it in their System Details but, wasn't reporting any problems with it.

If everything is working well you shouldn't worry about it.

Maybe someone more knowledgeable about it will toss in a comment.

You also still have the hotfix installed to add a new intermediate certificate for signing extensions that is no longer needed because this certificate is builtin.

• hotfix-update-xpi-intermediate 1.0.6 (hotfix-update-xpi-intermediate@mozilla.com)

When you type in the address bar about:studies you will see :

"cookie-restrictions-strict-list@shield.mozilla.org•Complete This study examines the effects of advanced cookie blocking. We may block extra cookies on some websites. The results of this study will help us to develop the next iteration of cookie blocking for all users."

Also see : https://github.com/mozilla/cookie-restrictions-strict-list-study