This is an older add-on that has been updated to work on later versions of Mozilla.
Session Manager saves and restores the state of all windows – either when you want it or automatically at startup and after crashes. Additionally it offers you to reopen (accidentally) closed windows and tabs.
This extension replaces SessionSaver and Tab Mix Plus’ session manager. It stores more data than both of them and should be more reliable in saving and restoring. Although it is not recommended to have more than one session related extension installed, Session Manager is compatible at least with Tab Mix Plus.
