You can search from the address bar in Firefox 4, but you won't get search suggestions as you type. If you want to change this, try: https://addons.mozilla.org/en-us/firefox/addon/omnibar/

(And you can use the "Customize toolbars" window to remove the search bar if you want.)

Firefox intentionally does not show suggestions in the address bar by default, because we don't want to send everything you type there to a third party.