New tabs are blank by default, there's no setting for changing that in Firefox. If you have something other than a blank page now appearing, an add-on you have installed changed the default action.

You can use this add-on to specify which page you want to open in a new tab.
https://addons.mozilla.org/en-US/firefox/addon/newtaburl/

Thank you very much.

You're welcome.

Please click the Solved It button next to the answer that answered or solved your Firefox support issue, it appears when you are logged in, so this thread gets marked as Solved to help other users who may have this same problem.