You appear to be at the "release-cck-sweetlabs" update channel according to the troubleshooting information you supplied, so it sounds that you have a special Firefox third-party build.

• https://ftp.mozilla.org/pub/firefox/candidates/67.0.4-candidates/build1/partner-repacks/sweetlabs/

Did you install Firefox from the Mozilla server?

Do a clean reinstall of the current Firefox release and delete the Firefox program folder before installing a fresh copy of the current Firefox release.

• download the Firefox installer and save the file to the desktop
  *https://www.mozilla.org/en-US/firefox/all/

If possible uninstall your current Firefox version to cleanup the Windows Registry and settings in security software.

• do NOT remove "personal data" when you uninstall the current Firefox version, because this will remove all profile folders and you lose personal data like bookmarks and passwords including personal data in profiles created by other Firefox versions

Remove the Firefox program folder before installing that newly downloaded copy of the Firefox installer.

• (64-bit Firefox) "C:\Program Files\Mozilla Firefox\"
• (32-bit Firefox) "C:\Program Files (x86)\Mozilla Firefox\"

• it is important to delete the Firefox program folder to remove all the files and make sure there are no problems with files that were leftover after uninstalling
• http://kb.mozillazine.org/Uninstalling_Firefox

Your personal data like bookmarks is stored in the Firefox profile folder, so you won't lose personal data when you reinstall or update Firefox, but make sure NOT to remove personal data when you uninstall Firefox as that will remove all Firefox profile folders and you lose your personal data.

• https://support.mozilla.org/en-US/kb/Profiles
• https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles

Reinstall Firefox

• https://support.mozilla.org/en-US/kb/troubleshoot-and-diagnose-firefox-problems

Thank you for your help. I have followed the instructions and reinstalled. I don't understand how I got that version in the first place, as I definitely installed it originally from mozilla.org. It seems to have happened in a recent update in June. How do I find out what that version was actually doing? What information it was recording? There seems to be no information about what it is.

I don't what is different in this special version. There are usually some extra files in the distribution folder to brand this version. They only have a version for Windows and I can't check this on Linux.