Firefox used XUL, not XAML. Still does, for some things that are not available in HTML. (By the way, you can enable devtools for the browser UI itself and take a look!)

XAML will be a target as we intend to build a WinUI3 client. Of the big three native targets: Apple, Android, Windows the later may be the easiest as from what I've seen nearly everything is in the template already

woah so this is like a react-native/expo done in a sane way ???? with swift?

damn