how to disable the autocomplete feature in firefox 3 and revert the location bar settings to Firefox 2.

As a part of Firefox 3, the Location Bar got a few upgrades. One of them is that it now uses a XUL richlistbox widget for the auto-complete dropdown. This means that typing in the Location Bar will now search not only URLs, but page titles, bookmark names, and tags. A drawback to this new feature is that if you start typing something like google in your Location Bar, the things like thepiratgoogle will show up (assuming you’ve visited that site, have it bookmarked or its title is in the URL you’ve previously visited. While many folks (myself included) like this feature, some do not. This brief tutorial will show you how to disable that feature.

1. To get started, enter about:config in the Firefox Location Bar
   
2. Click the I’ll be careful, I promise! button.
3. In the Filter: bar, enter browser.urlbar.matchBehavior
   
4. Under Preference Name, a browser.urlbar.matchBehavior line should appear. Double-click it.
   
5. Change the entry from 1, to 2. Click OK. You can close the about:config window/tab (or just visit another page).
   
6. Now when you enter something like google in the location bar, only ebay domains will show up.

credit: http://www.simplehelp.net/2008/06/18/how-to-revert-to-the-firefox-2-autocomplete-location-bar-settings-in-firefox-3/