The phrase, "This may void your warranty" appears when you type "about:config" into your Firefox address bar. Firefox's about:config page may be relatively unknown, but you can use it to tweak your browser and make Google the default search engine for Firefox's address bar. After you update about:config, type any query into the address bar to send the query to the Google search engine.
You use the values stored in about:config whenever you launch Firefox. About:config contains the preferences settings that control Firefox's appearance and the way it operates. The "Font" settings, for example, define the fonts the browser uses to display various menus and controls. Although a file named prefs.js contains your actual preference settings, the about:config page allows users to update those settings safely from a convenient Web page that displays in the browser.
Accessing About:config Settings
"About:config" may seem like an unusual phrase to type into Firefox's address bar, but when you do that and press "Enter," the about:config page opens. This page contains a search box and a table. The table contains preference names in one column and their statuses in another. An additional column shows the value of each setting in the table. You have the ability to change these values and add new ones. To make Google the default search engine for the Firefox address bar, you must update the setting that defines the bar's default search.
All updates to about:config work the same way: find the setting you wish to update, and change it's value. About.config's table contains dozens of settings. Searching for a particular one manually may take time. To find the setting you need to update, type "keyword:URL" into the search box that appears at the top of the page. Firefox returns the setting named "keyword:URL." Double-click that setting, and type "http://www.google.com/search?q= " -- without the quotes -- into the text box that appears. After you do that, Firefox updates your preferences and changes its address bar's default search engine to Google.
Try out your new search settings a regular search query into Firefox's address bar. Firefox recognizes your text as a search query and launches a Google search. Results will appear in a new window or tab depending on your browser settings. If you make a mistake pasting or typing the Google URL into the about:config settings window, searches may not work when you type queries into Firefox's address bar. Correct this problem by double-clicking the "keyword.UFRL" preference name again and pasting it in the correct Google URL string.