My favourite Firefox Tweak from using about:config is the parameter: browser.sessionstore.max_windows_undo I change this from from 3 to 20 For days on end I often have about 20 Firefox Windows open and each with about 10 to 20 tabs. With browser.sessionstore.max_windows_undo set to its default of three, if I crash or need to reboot, then on restarting I can only get three previous Firefox windows to re-open. The other 17 are not available. After a reboot I launch Firefox and because I have... Settings--> Preferences--> General--> Startup--> Restore previous session (checked) One Firefox window opens with its previous tabs available. On the Firefox menu bar I then click on... History--> Recently closed Windows--> ...which will show my recently closed windows. This is where I click on "Restore all Windows" and get the other 19 x previous Firefox Windows and their tabs to open. cheers, Ian.