@temor Normal re-installation methods do not remove profile data, meaning extensions/add-ons will not be removed. If you are technically literate and know for a fact you did a clean install, or if you don't care about switching computers, stop reading here. It's a waste of your time.
In the event that you do use some form of add-ons/extensions, and haven't done a clean install. You may wish to try restarting in safe mode(all add-ons disabled)
https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode#w_how-to-start-firefox-in-safe-mode
If this doesn't work, stop here. Your computer is haunted.... (or something more technical sounding. I don't believe it is worth the time trying to solve)
If that does work, you could consider doing a refresh described on the same page. That will put you in factory state, meaning all add-ons and settings will be removed, but bookmarks, history, and passwords will stay with you.
If when you reinstalled, you clicked the tiny checkbox that said something like "also delete all user's profile data" , this shouldn't be necessary. But normal installs/uninstalls don't mess with your profile data unless you explicitly request it to.