Location bar search

Excerpted from:
http://support.mozilla.com/en-US/kb/Location+bar+search

If you enter text into the Location bar that is not a valid Internet address (URL), Firefox will try to direct you to the location you intended.

Internet Keyword search

1. about:config
2. keyword.enabled
• false disables Internet Keyword searches.
• true enables Internet Keyword searches.
  

Domain Guessing

1. about:config
2. browser.fixup.alternate.enabled
• false disables Domain Guessing.
• true enables Domain Guessing.

References

Customising the Firefox 3 Location Bar. • mozillaZine Forums
http://forums.mozillazine.org/viewtopic.php?f=38&t=685365