Is it possible that you've experienced [https://www.ghacks.net/2019/06/14/if-you-lost-all-passwords-in-firefox-read-this/ this problem]? It can happen most commonly when you are running either Avast or AVG (both the same company), but there are some other security programs that may cause similar issues. Of course, that's assuming you've only lost your logins and passwords. If you've lost everything (bookmarks, etc), then the [[Recover lost or missing Bookmarks]] page will probably be more helpful for you. Hope this helps.