Previously it used to perform a Google “I’m Lucky” Search and take you to the first page of its search results automatically.

If you want to restore the Google “I’m Lucky” search then perform this simple steps:

1. Type

   about:config

   in your Firefox location bar and press Enter

2. Type keyword in Filter textbox and you will see only the preference keyword.URL.
3. Double-click on keyword.URL and change the value to:

   http://www.google.com/search?btnI=I%27m+Feeling+Lucky&q=
   

4. You’re done!
   

That’s all it takes to restore default keyword search functionality in Google.

Note: You can use this to change to any search engine for keyword search.

Original article:  How to Change Your FireFox Location Bar Search Engine.