In Firefox, if you type some words into the address bar instead of a URL, Google is used as the default search engine to search with those words as keywords. To change this default search engine, open
about:config, go to
browser.search.defaultenginename and change its value to the name of the search engine you want. For example, changing
Make sure that the plugin of the search engine is already installed in Firefox. For example, in Firefox 4.0 I found that Google, Yahoo and Bing plugins were already installed. For more information see the MozillaZine page on about:config entries.
Tried with: Firefox 4.0