Let’s do a full clean re-install;

Note: Firefox comes in three or more folders on all computers. They are;

Maintenance: (Programs Folder) <Windows Only> Firefox itself: (Programs Folder) And two folders in the profile of each user on the computer for each Firefox profile for that user.

If you remove the Firefox folder, the user profiles would not be affected.

Download Firefox For All languages And Systems {web link}

Save the file. Then Close Firefox.

Using your file browser, open the Programs Folder on your computer.

Windows: C:\Program Files C:\Program Files (x86) Note: Check Both Folders

Mac: Open the "Applications" folder. https://support.mozilla.org/en-US/kb/how-download-and-install-firefox-mac

Linux: Check your user manual. If you installed Firefox with the distro-based package manager, you should use the same way to uninstall it. See Install Firefox on Linux; https://support.mozilla.org/en-US/kb/install-firefox-linux

If you downloaded and installed the binary package from the Firefox download page, simply remove the folder Firefox in your home directory. http://www.mozilla.org/firefox#desktop ++++++++++++++++++++++++++++ Look for, and remove any Mozilla or Firefox program folders. Do not remove the Mozilla Thunderbird folder if there is one.

Do Not remove any profile folders.

After rebooting the computer, run a registry scanner if you have one. Then run the installer. +++++++++++++++++++++++++++ If there is a problem, start your Computer in safe mode and try again.

http://encyclopedia2.thefreedictionary.com/Linux+Safe+Mode This shows how to Start all Computers in Safe Mode; Free Online Encyclopedia

Try to rename/remove compatibility.ini in this profile folder with Firefox closed.

You can use the button on the "Help -> Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the about:profiles page.

• Help -> Troubleshooting Information -> Profile Directory:
  Windows: Show Folder; Linux: Open Directory; Mac: Show in Finder
• http://kb.mozillazine.org/Profile_folder_-_Firefox

Thanks @FredMcD. I have done a clean reinstall as you suggested, and have to wait until next new version to see if it has resolved the issue.

When scanning, the C:\Windows\Logs\CBS\CBS.log issues warnings about WindowsPowerShell and other issues not related to Firefox (wallpaper, Windows Defender etc.), so that should be good.

Even though removing the Mozilla Firefox folder, when reinstalling Firefox, Firefox mentioned that a prevous Firefox was discovered, and provided the option to reinstall, which I did. I don't know if this is just because it discovered my user profile.

For now, I will wait until next update, to see if the issue is resolved. Thanks.

Henrik

Note that Firefox 68.0.1 has recently been released.

• https://www.mozilla.org/en-US/firefox/68.0.1/releasenotes/

I have this same issue. It has happened now at least 10 times. I think I have found a solution for it, although I really don't want to do it: import all bookmarks into Chrome...

Really frustrating. I work on Windows Server and I cannot just reinstall software.