Have you been using Firefox Sync (this is enabled when you have been signing your Firefox in to a Mozilla account)? Did you lose any other data such as bookmarks, history, settings, etc.? Check the following article for that scenario: [[Recover user data missing after Firefox update]]. There may sometimes be a problem in the '''logins.json''' file which causes Firefox to set it aside under the file name '''logins.json.corrupt'''. You could check your profile folder to see whether you find that file. To access the folder: [[Profiles - Where Firefox stores your bookmarks, passwords and other user data]].