Try creating a new profile. In the first article linked below there are sections telling you how to open the profile manager with Firefox open or closed. https://support.mozilla.org/en-US/kb/profile-manager-create-remove-switch-firefox-profiles ---- See the other articles for copying data from the old profile to the new profile. You need to do that with Firefox closed. https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data#w_finding-your-profile-without-opening-firefox