If you are concerned about your privacy, you can turn this feature off completely: 1. In the Location bar, type about:config and press Enter. * The about:config "This might void your warranty!" warning page may appear. Click I'll be careful, I promise! to continue to the about:config page. 2. Type browser.newtab.url in the search box. 3. Double-click the browser.newtab.url preference and change the url from about:newtab to about:blank. Alternately, you can change it to about:home for the Firefox Google home page, or type in your preferred home page, for example google.com. 4. Click OK and close the about:config tab.
which is designed to improve the first-time-with-Firefox experience.