Source: http://feeds.gawker.com/~r/lifehacker/full/~3/313034717/search-saved-passwords-in-firefox-3
Trying to recall which username and password you use for which web site, or if you even have a log in to begin with? Firefox 3 includes a built-in search function for the saved passwords.
To check it out, go to Tools, Options and then the Security Tab. Then click on the "Saved Passwords..." button under the Passwords section.Enter a full or partial search term and find that elusive username and password. (Firefox 3's official release is scheduled for tomorrow, June 17th.)
Search Through Your Saved Passwords [Firefox Facts]