Firefox is not able to remember where you left off the last time you were using it. This is normally not a big deal if you are able to close firefox after you´ve done what you wanted to do. The problem begins when Firefox crashes or when you have to turn off your computer in a hurry. Session Saver is able to save the current state and restore it at a later time. Session Saver saves tabs, window positions, text in websites and cookies for example
This is not only great to prevent data loss through crashes but also nice if you have websites that you visit together. Say you have a set of three websites that you visit once a day regulary. Save the session when all three websites are open in their own tab and restore them the next day right where you left oft.
If you experience slowdowns or hangs after using session saver for a while you might want to check the file of pref.js which stores all your sessions. As a rule of thumb, the bigger the file the slower firefox will be. Delete old sessions to reduce the file size and speed up things again.
You also should consider to reduce the number of tabs if you experience regular slowdowns. This happens when Session Saver saves the session to the file on your hard disk. If you have 50+ tabs this could take a while, consider reducing the tab amount and everything should be running smoothly.

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Firefox App Tabs Add-On
Web Browser: Firefox Save Tabs Add-On
Been using the session saver for ages now and I’m more than satisfied with it. Lucklily, Mozilla is including this feature in the 2.0 release of Firefox.
Tab Mix Plus is another extension that will do this.
Firefox 2.0 has this feature already, but I’ve been using Google’s Browser Sync extention for a while now to do this. It can save sessions across multiple computers.
Permanent data loss will be approved.
Thanks too much!@