• Go to Tools -> Options or the Firefox Menu -> Options.
• Set When Firefox starts to 'Show my Home page'.
• Set Home Page to 'about:newtab'.

Type about:config in a new window address bar. Click 'I will be careful'. You will see all kinds of information that Firefox uses so it knows how to work. There is a search bar at the top of the page. Type 'browser.startup.homepage' and check its entry. You can change it to what ever web page you want, or you can enter; 'about:blank' for a blank page. I use the Firefox home page; about:home. After, go back to the search bar and type; browser.newtab.url. This is what a new tab page will display. Do the same thing here. You can have the same for both or have each open to different pages.