Description:

Building upon SessionStore, this extension allows you to save the current state
of Firefox (history, text data, cookies) and return to that state at any later
moment. Besides the manually saved states, Session Manager automatically stores
the current state in case of a crash.

All sessions are stored in the "sessions" folder inside your profile directory
and can be moved around as any other file. To get to that folder, simply select
"Open Session Folder" in Session Manager's menu (might not work on all OSes).
Finally, Session Manager also allows to reopen the 10 last closed windows and
tabs.