You can't set a Custom URL for New Tab

But you can Customize items on your Firefox New Tab page to display a Web Search, Shortcuts to your most visited sites, Recommended stories and other information. You can choose what to display so the page feels just right for you.

New Tab page in Firefox

Thanks for your fast reaction ! OK , accepted for NewTab, I never paid attention to it I think ... But when starting FF by double-clicking the icon on the desktop, FF does not open the URL configured in Settings/Home/New Windows and Tabs. I used another User at Win11 logon and installed FF there. On that (fresh) installation, FF opens the URL as it should. What could be wrong with my main FF installation pls ? In attach a print-screen from the configuration and the "start-up-screen" of the other user Thanks

Did you check the Firefox startup setting in "Settings -> General (Algemeen)" as you may have set Firefox to restore the previous session ?

Use one of these to close Firefox if you are currently doing that by clicking the close X on the Firefox Title bar, especially if you have multiple windows or Private Browsing windows open to prevent losing tabs in unnoticed windows.

• "3-bar" menu button -> Exit (Power button)
• Windows: File -> Exit

If necessary, check "History -> Restore Previous Session" and "History -> Recently Closed Windows/Tabs".

• https://support.mozilla.org/en-US/kb/restore-previous-session