*
      enter "about:config" in the address bar to get the list of user preferences
    *
      type "browser.startup.page" in the filter
    *
      right-click to modify the value from 1 to 3  (1 is the default that opens the browser to the homepage only; 3 is the setting that tells Firefox to always restore the previous session)


From there You can shut down firefox and it will auto restore the tabs even tho you closed them. :-)