On a Mac you can see if you can find a copy of the sessionstore.js file in the Time Machine from around that time and restore that file to the Firefox profile folder. I don't know if such files get saved as well. If not then you are out of luck. *http://kb.mozillazine.org/Session_Restore *https://support.mozilla.org/kb/Session+Restore *https://support.mozilla.org/kb/Recovering+important+data+from+an+old+profile *http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox