Session Manager saves and restores the state of all or some windows -- either when you want it or automatically at startup, after crashes or periodically. It can also automatically save the state of open windows individually.
This extension replaces SessionSaver and Tab Mix Plus' session manager. It stores more data than both of them and should be more reliable in saving and restoring. Although it is not recommended to have more than one session related extension installed, Session Manager is compatible at least with Tab Mix Plus. It can import sessions from both SessionSaver and Tab Mix Plus.
Download Session Manager Firefox Add-on
You can download Download Session Manager Firefox Add-on from here