Here's a little workaround for it:
In about:config page, change these keys:
browser.urlbar.matchOnlyTyped = True
browser.urlbar.matchBehaviour = 2
browser.urlbar.maxRichResults = (max results, put between 2-5)
browser.urlbar.search.timeout = (search timeout, put something lower than 100, depending on ur needs)
This little tweak did the job just-right for me.
Recommended reading: A little bit googling for "Firefox 3 addressbar tweak" lead me to this one nice article: CyberNotes: Understanding & Tweaking the Firefox 3 Address Bar.