HowTo: Turn this feature off completely
In the Location bar, type about:config and press Enter:
about:config
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. Type browser.newtab.url in the search box:
browser.newtab.url
Double-click the browser.newtab.url preference and change the url from about:newtab to about:blank Click OK and close the about:config tab.
about:blank
The post where I got this information is here
http://www.cyberciti.biz/faq/howto-mozi ... -tab-page/