Check out the keyboard shortcut goodness… use J and K for next/previous results, O to open and / to move back to the search box (extremely cool for when you don’t find anything with the first search)

I’m sure that Google or somebody else will eventually release a search plugin that enables this by default.

Update:Thanks to Gina @ Lifehacker, you can get the plugin goodness without having to manually modify anything. My technique still works, but it’s probably easier to use Gina’s plugin.

If you still want to do it manually, navigate to your Firefox installation directory, and open the searchplugins folder.

 

Essentially all we’re going to do is add the bolded line to the google.xml file, which you can download here, or edit it yourself.

—- snipped for length —-

Make sure you backup the existing file before you replace it with this one, restarting Firefox when you are done.

You can see that the search suggestions still work, but now you will be sent to the experimental search instead of the regular one. 

Thanks to Lifehacker for pointing me to this one.