Do you know how this happens? 1) Look on your desktop. Do you see a folder called; '''Old Firefox?''' Look inside. Look for the folder with the latest creation date. https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles https://support.mozilla.org/en-US/kb/how-run-firefox-when-profile-missing-inaccessible

2) https://support.mozilla.org/en-US/kb/how-run-firefox-when-profile-missing-inaccessible http://kb.mozillazine.org/Profile_folder_-_Firefox#Navigating_to_the_profile_folder https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles Type '''about:profiles'''<enter> in the address bar. How many profiles are listed? How many should be there? Also, open the folder in your file explorer.

You can also look for a C:\Windows.old folder. *https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile