Session Manager can save, backup, restore, and manage multiple Firefox tab sessions. It comes with the option of loading the last saved session, not loading a previous session, loading a specific older session, or asking for the user to choose. Already, that makes it more powerful than the native Firefox session manager.
In addition, it can save any number of older sessions, configurable from the main window, and gives users several options for session management when Firefox is shut down. The plug-in automatically backs up sessions in the event of a crash. Users can also configure how the add-on displays the list of saved sessions, merge new and old sessions on recovery, and reload tabs on recovery.
Finally, there are some nifty options for power users in Session Manager. You can configure how the sessions are named, change the default saved sessions location, encrypt saved session data, and configure how postdata gets saved, even from encrypted Web sites. Since each session file created by Firefox includes text data, cookies, and history, as well as tabs, being able to recreate all that information effortlessly is a major headache remover that shouldn't be underestimated.