Firefox: If you're on a netbook or just want some more vertical space, Firefox extension OneLiner condenses Firefox's toolbar by putting everything on one line.
If you like the look of Internet Explorer 9's condensed toolbar, you'll love OneLiner for Firefox. By installing the extension (which is, by the way, restartless), you can consolidate your navigation bar and tab bar into one bar along the top. You can already do this with the "Customize Toolbars" option in Firefox, but this makes it a one-click process, which is perfect if you don't want it that way all the time. It also adds a simple button for search in place of the original search box, hides the back and forward buttons when not in use (so you can see more of the URL), and more small tweaks. Hit the link to read more.
OneLiner is a free download, works wherever Firefox does.