By default, when you type in keyword(s) in Firefox address bar, it will search the keyword(s) using Google Search and lists matching websites.
To change the Firefox option is very simple, as follows:-
At Firefox address bar, enter about:config and press ENTER.
You will see a warning as below
Click "I will be Carefull, I Promise!" Don't worry the below step has been tested on firefox version 13.0.1 and would not create any issue.
At Filter: field, type keyword.url
You should see a Preference name of keyword.URL in the list. Double click it, a “Enter String Value” input box will appear.
Replace the string with:
Click “OK” button and done!
You can replace the string value with any search engine query that you know. Example for Yahoo! search: