'Registry Repair', and 'Session Manager'

Registry Repair

Almost all Windows users gradually experiences the downfall in their PC's performance. Much of it can be attributed to Windows Registry Errors. By using Free Window Registry Repair regularly and repairing your registry, your system should not only be more stable but it will also help Windows run faster. For your convenience it automatically backs up any repairs made so that you always can restore Windows registry to the original state.

http://www.regsofts.com/

Session Manager

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.

http://sessionmanager.mozdev.org/