Web extensions can't do this in current Firefox releases (bug reports mention about: and file: links, but I assume that chrome: doesn't work as well). An alternative could be to set the homepage and middle-click the toolbar Home buttom (you can drag this button to the Tab bar).

This is still possible directly via other ways. You can paste this code in the Browser Console to see this working.

var newTabURL = "chrome://browser/content/places/places.xul";
aboutNewTabService.newTabURL = newTabURL;

Set devtools.chrome.enabled to true on the about:config page to enable the command line or use the settings page (F1) of the developer tools.

• https://developer.mozilla.org/en-US/Tools/Browser_Console

thank you everything is working!

but after closing the browser, this var newTabURL = "chrome://browser/content/places/places.xul"; aboutNewTabService.newTabURL = newTabURL; disappears.

zig-zag said

but after closing the browser, this var newTabURL = "chrome://browser/content/places/places.xul"; aboutNewTabService.newTabURL = newTabURL; disappears.

Yes, that little snippet of script makes a dynamic change to Firefox's behavior, but only for the current session. At the next startup, Firefox reads the saved settings as usual.

Some little bits of script can be run automatically at startup using an Autoconfig file, but over the past year, the things that file is allowed to do have been restricted, since they were abused by other software, so I don't know whether it can still make that change.