Tab Mix Plus enhances Firefox's tab browsing capabilities. It includes such features as duplicating tabs, controlling tab focus, tab clicking options, undo closed tabs and windows, plus much more. It also includes a full-featured session manager.
TooManyTabs allows you to store as many tabs as you like by adding extra rows in the Firefox! It saves your browser's space and memory as idle tabs are put aside. The extra rows also help to better prioritize and visualize your tabs.