Among the changes in Firefox 2 is that the ‘Go’ button is now attached to the address bar, when customizing toolbars. Some Firefox users may prefer not to display the ‘Go’ button, because they use the |Enter| key, or use the Paste and Go 2 extension.
You can get rid of the ‘Go’ button by entering about:config in the address bar. In the resulting page, search for the preference browser.urlbar.hideGoButton.
Double-click on it, which should change the value to true.