For users of Firefox 4 that open many tabs don’t forget to select arrangement “Show my windows and tabs from’s Last time” at arrangement of your firefox 4.0. Is important for you which when browsing opened many tabs. Of course you do not want to lose site addresses that you have not saved and these also able to happen if your firefox experiences crash.
Firefox 3 which when want to close or firefox experiences crash will show notification want to reopen all tabs that had been opened and repeated its again later, then in Firefox 4.0 has no notification as such. But to overcome it, you can to change arrangement in your firefox 4 like below.
Open Your firefox’s arrangement at menu : Tools > Options. Then change Startup’s arrangement from Show My Home Page becomes Show my windows and tabs from last time. The next Save / Ok