Firefox 3 has an annoying new URL bar that takes up about 75px in screen real estate for each auto-completed URL. It’s referred to as richResults in about:config. In the previous beta releases you were able to manually add a preference to remove this feature. As of firefox 3 beta 4 (or maybe beta 3, i didn’t install that release) this no longer works for whatever reason.
If you prefer the old style urlbar, you need to install the oldbar extension. https://addons.mozilla.org/en-US/firefox/addon/6227