1. Removing and reinstalling Thunderbird and Firefox rarely fix anything.
2. In either case, you do not lose data, extensions, settings, mail, etc., which are all kept in their related profiles, not in the program files.
Profile folder - MozillaZine Knowledge Base
3. If TB opened in Safe Mode, which is a troubleshooting mode and is not intended to be used otherwise, can you now open TB normally? For reasons that are unknown, there are times that using Safe Mode fixes problems just by its being used, and one can then return to non-Safe Mode operation.
4. If TB will not start in normal mode, try removing the TB extension folder from the TB profile; it is possible, albeit nor very likely, that one or more extensions have become so corrupt that they it/they are preventing Tb from running.
5. The next step would be to create a new Tb profile, and transfer folders and files from old to new one at a time, and testing each one.
6. If all else fails, then you likely need to invoke whatever spirit moves you, do whatever magic dances and/or incantations are appropriate, or create a medieval scriptorium for hand-written replacement documents for e-mail.
