The <b>browser.newtab.url</b> pref is no longer supported in Firefox (41+), so it is no longer possible to set the new tab page via this pref. You can look at this extension to set the new tab page: *New Tab Override: https://addons.mozilla.org/firefox/addon/new-tab-override/ You can set the new tab URL via the Options/Preferences of the extension on the about:addons page. You can look at this extension if you use the home page as the new tab page. *New Tab Homepage: https://addons.mozilla.org/firefox/addon/new-tab-homepage/ Classic Theme Restorer includes this feature as well. You find "New tab page url" in the Tabs (2) section. You can use pages like these: *the default new tab page with the tiles is <b>about:newtab</b> *the default home page is <b>about:home</b> *for a blank page use <b>about:blank</b> *for Super Start use <b>about:superstart</b> *use the URL of a web page See the <b>about:about</b> page for available about pages.

Thanks - this was what I was looking for: New Tab Homepage: https://addons.mozilla.org/firefox/addon/new-tab-homepage/