As an emacs user, I've found iswitchb (interactive-switch-buffers) to be a huge time saver. Basically, to switch files (buffers) you enter a typically byzantine key combination and then type to search through your open files - as less and less files match your search, the choices narrow down, and you can choose between them. This ends up being way faster than switching with a mouse even in tabbed editors, and I've managed to set up a similar thing in Eclipse/Aptana. But until recently I didn't have the same functionality for switching tabs in Firefox.
The good news is that Firefox 3.6 has this feature built in, though it takes a bit of work to enable. Apparently they've been trying to get this feature into Firefox since 3.0, but there's been a lot of different opinions, so even though they finally shipped it with 3.6, it isn't on by default. You can turn it on by going to about:config (just type that right into your address bar), then searching for “ctrlTab”. Double-click browser.ctrlTab.previews to turn it to “true”. Now, when you hit Ctrl-Tab, you'll get a tab switcher that looks a bit like the default Windows Alt-Tab window switcher (though with a much lighter glass effect that honestly looks pretty bad compared to Windows' Alt-Tab). On other platforms you'll get a similarly system-integrated look. Unfortunately this popup isn't exactly what we're looking for - it doesn't show all your tabs and you can't search! However, you can navigate down to “show all X tabs” at the bottom and you get a search box and a list of every tab. That's a real pain to do every time you want to switch tabs, though. Fortunately, there's a solution. Instead of hitting Ctrl-Tab, use Ctrl-Shift-Tab, and you'll start out right at the big tab switcher with search. From here you can type to narrow down your selection and hit Enter to choose your tab. I wish there was a preference to make this full search show up when you hit Ctrl-Tab, but it doesn't look like there is.
Visual issues aside, I wish every program with a tab-oriented UI had a feature like this to make their app faster to use for keyboard users. While we're at it, Windows and OSX should add search to their built-in window switchers - it could really help when I have a lot of windows open and don't want to reach for the mouse.
Note: There are a couple extensions for Google Chrome that theoretically give a similar searchable tab switcher, but of the few I tried, none of them could appear with a keyboard shortcut - you had to click an icon on the toolbar, which seems to defeat the point. Apparently the Chrome Extensions API has known problems with keyboard shortcuts, so maybe things will get better soon.