Edilee who made Account Manager for Firefox 4 which simplifies sign-in process on websites (Account Manager not shipping with Firefox 4 final), developed QueryStats add-on for Firefox 4 which shows the queries you searched in Firefox search bar.Moreover to install this add-on  in Firefox 4 user doesn’t required to restart Firefox and this add-on will be automatically uninstalled once it ran.

This add-on scans for queries you searched in Firefox search bar and groups your searches by words you typed.First set shows unique search queries which you performed, second set shows repeated search queries.

After installing QueryStats, results will be shown in new tab.

You can try QueryStats add-on latest Firefox 4 beta .(via)