Hello Steve. If you lost the whole of your personal information (including home pages, settings, bookmarks, passwords, history, add-ons and so on), ''absolutely'' everything, and all has come back to "factory defaults", per say, it's possible that your profile is no longer being used. To know more about Firefox profiles, see this: http://support.mozilla.com/en-US/kb/Profiles To know how to manage profiles, see this: http://support.mozilla.com/en-US/kb/Managing+profiles Those two pages are easy to understand and should tell you all you need to know to get your profile back. If you have any question, feel free to ask. It's also possible that your profile was simply erased (for whatever reason, Firefox wouldn't do that, but third party software or even the user may do that, either inadvertently or on purpose), and if that's the case (basically, if there's no folder in your profiles folder with your profile), there's nothing to be done.