One option is to explain your problem and someone may be able to assist. Or, you can start over by doing this: - click help>troubleshootinginformation - scroll down to 'profile folder' and click 'open folder' - exit thunderbird - delete the file prefs.js - restart thunderbird

There is a way to start with a fresh profile without affecting the current profile, in case it has things you wish to keep, such as address books or local mail. Help/Troubleshooting Info, about:profiles, and create a new profile (assuming you're not using the MS Store version of TB).

sfhowes is the method of starting with a fresh profile without affecting the current profile the steps shown in David's post above? Or will that wipe out my address books?

Deleting prefs.js won't remove the address books, but it might make them not recognized. If the profile is corrupted, I recommend creating a new one. Address books can be transferred from the old to the new by copying abook.sqlite and history.sqlite, with TB closed. Or, from Tools/Import...