Watch the video down, by Mozilla’s excellent interface designer Aza Raskin, for a quick overview. The idea is sort of like the new app folders in iOS 4, or like a better version of OS X’s Exposé—except for it’s all about your browser tabs. You can drag and drop to re-arrange all your tabs into groups, create new groups by simply dragging a web page outside an existing group and dragging another item on top of it, and name all your groups based on what task they’re related to.
An Introduction to Firefox’s Tab Candy from Aza Raskin on Vimeo.