If you frequently use multiple tabs when you use Firefox, you'll want to immediately download FoxTab (free), which offers a great set of tools for handling many open tabs. It makes it easy to find the tab you want fast, see what you have open at a glance, see closed tabs, and much more.
When you install FoxTab, it adds a new icon to the left of the Firefox address bar. Click it and you'll see thumbnails of all of your tabs in a 3D view that looks much like the Windows Vista-Windows 7 3D Flip feature. Scroll through them all until you find the one you want, then click it to go there. You can change the angle and direction of the view, and choose the background color as well. To leave the FoxTab view, press the Esc key, or click the FoxTab icon again.
That's just the beginning, though. FoxTab offers far more powerful tools than just a 3D look at your open tabs. You can also arrange them in other ways, including as flat thumbnails on a variety of different grids, and in a nifty view that looks much like the Mac's Cover Flow feature. You can also show tabs that you've recently closed. And you can also search through the titles and URLs of open tabs.
Its Top Sites feature is an excellent one as well. Top Sites works and looks much like Safari. When you open a new tab, instead of seeing a blank page, you see 3D thumbnails of your favorite sites. Just click any to get to it. One drawback to this feature is that unlike in Safari, the Top Sites feature doesn't populate itself based on sites you've already visited. You'll have to FoxTabs which to put there.
There's one more drawback to FoxTab: It doesn't play nice with Firefox 4's new Panorama tab-handling capabilities. If you click Firefox's Panorama icon to launch Panorama, the Panorama page launches behind FoxTab so it's not visible. In addition, FoxTab won't show you the tabs you've grouped together in Panorama.
Still, FoxTab is a very useful tool if you're not a fan of Panorama. You'll find it to be a very useful tab-tamer.