I downloaded FoxTab a few days ago and love the way it works. It has views similar to both Cover Flow and Expose on a Mac, giving a miniature image of each of the tabbed windows you have open in Firefox. Highly recommended.
Windows only: Experimental Firefox extension FoxTab introduces a new tab switching interface to Firefox complete with five different thumbnailed views. Firefox already has a new Ctrl+Tab switching interface in the works for the 3.1 release with the Ctrl+Tab extension, and FoxTab tosses another attractive hat into that ring. FoxTab views include several familiar ideas, like Vista's new Flip 3D or OS X's Cover Flow—but for your Firefox tabs. FoxTab is a free experimental plug-in (which means you need a username and password to download it from Mozilla Add-ons) and it runs in Firefox.
FoxTab [via Mozilla Links]