That message when logging into this forum is common, it's a glitch in the underlying forum software.
All forums running on the 'Invision Community' sofware are currently seeing it.
I get it everyday both here and at the Malwarebytes forum which runs on the same software.
So it's not your machine or CCleaner, it's something that Invision need to patch.
To get back to the 'need to close the browser' message.
You did say that CCleaner "CCleaner doesn't usually perform like this", so was this just a one-off or has it started happening regularly?
One though I had if it was a one-off, was there a Firefox update pending? ie. downloaded but waiting for Firefox to be launched again before it installs.
You can check if you are signed in to a Firefox account (and syncing) by clicking the hamburger icon, you can see here that I'm not signed into one:
![image.png]()
HTTPS everywhere shouldn't keep running once Firefox is closed.
BTW that extension is no longer needed, the function is now built into Firefox. Go to Settings>Privacy & Security and scroll to the bottom of the page.
I don't use Privacy Badger but wouldn't have though that would continue running after Firefox is closed.
If you keep getting that message from CCleaner then you could try temporarily disabling PB to see if it makes a difference.
If this is a recurring message that you are getting from CCleaner then there are a couple of things you can try in Firefox, such as running it in Safe/Troubleshoot Mode to rule out any interference from add-ons or Firefox/Windows settings.
If running FFx in Safe Mode stops the problem then you know that it's an add-on or setting that is causing it.
https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems
I don't think that your FB oddity with the 2FA is related, reading around it seems that FB's 2FA does throw up issues like that from time to time.