In previous versions of Firefox, there was an extension that performed this function but now Session Restore is part of the main functionality of Firefox. This is very convenient because if you browse a lot and you don’t want every time you start your browser to start your search from the beginning, you can select the Show My Windows and Tabs From Last Time option in the Startup section of the Main tab in the Options dialog box and when you start Firefox, your tabs and windows from the last time will be waiting for you.