Tabs Outliner - Next Generation Session, Windows, Tabs Manager and a TooManyTabs Solution That Really Works.
Tab Utilities - Tab Utilities is an ultimate tab solution for all kind of users who want to manage their tab, create multiple session and search for new tabs, etc.
Undo Closed Tabs Button - Add a toolbar button onto any toolbar to undo closed tabs
Session Buddy - Manage Your Browser Sessions
Tree Style Tab - Tree Style Tab is an all-in-one Firefox extension that provides ability in order to operate tabs as a tree.
Tab Tally - Firefox add-on, displays how many tabs are open.