Hi, sorry to hear that. You sure it was Firefox as Windows Update can do something like this also. Please see if there is a Folder on your Desktop called OldFirefoxProfile if so it may be possible to get from that. Also please check here for the oldest dated profile : *https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data If it is found : you can transfer files from a previously used profile to the new profile, but be cautious not to copy corrupted files to avoid carrying over the problem. Never work with original files. *https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile *http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox If not there is no recourse. You may want to try a Windows System Restore Point but not sure that will help much. Please let us know if this solved your issue or if need further assistance.