Here at CNET Download.com central, we love Tab Mix Plus. It's so close to perfect, but the one thing it lacks is a decent method for restoring lost multi-tab sessions. Crashes can often lead to important tabs being irrevocably lost. Lucky for us all there's the Session Manager plug-in, a stand-alone extension that, when used with Tab Mix Plus, bestows the power of resurrecting dead multi-tab sessions to all us hapless tab abusers.
The easiest way to run Session Manager with Tab Mix Plus is to disable TMP's session recovery. It can only save two sessions, and lacks the customization specifics of Session Manager. SM 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 TMP or Firefox managers.
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 shutdown. The plug-in automatically backs up sessions in the even 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.
Users who don't want to use Tab Mix Plus but like Session Manager also get the ability to restore closed tabs from Session Manager, and can configure how many closed tabs the plug-in can remember. As with the session lists, the behavior of the closed tabs list is configurable. Personally, I don't use it because I like the TMP one, but it's good to know that there's an alternative if I ever get obsessive about my closed tabs.
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, so being able to recreate all that information effortlessly is a major headache remover that shouldn't be underestimated.