Type about:config<enter> in the address bar. If a warning screen comes up, press the Be Careful button. At the top of the screen is a search bar. Type browser.newtab.url This tells Firefox what to show when a new tab is opened. If you want, right click and select Modify. You can change the setting to;

about:home (Firefox default home page), about:newtab (shows the sites most visited), about:blank (a blank page),

or you can enter any web page or about: page you want.

The same instructions are used for the new window setting, listed as browser.startup.homepage.

hi, you can change the new tab page (the default is about:newtab) like this: enter about:config into the firefox address bar (confirm the info message in case it shows up) & search for the preference named browser.newtab.url. double-click it and change its value to an url of your choice. this method will work until firefox 40 - after that you have to use https://addons.mozilla.org/firefox/addon/new-tab-override/

(edit: too late…)

Thank you Fred. Worked perfectly.