Tab Kit is a Firefox add-on that makes tabs more efficient for power users, bringing comprehensive tab grouping, and tweaks such as multiple rows of tabs or displaying tabs as a tree. Tab Kit will keep each tab wide enough for you to view a preview of the page titles. It achieves this either by letting you roll your tabs over into a second row of tabs. Or a third or fourth row, if you don't mind losing some more screen real estate.
But that's just the tip of the iceberg. Tab Kit will also let you move all of your tabs over to the Windows sidebar, or to the bottom of your screen.
Tabs, Firefox, Addon, Add-on, Extension