Yes, this is a nice thing. But it supports way fewer features a modern web site could legitimately use.
The modern browser engine exposes a lot of controls to scripts and to the chrome layer. IIRC Firefox uses this extensively to code (most of) the UI in Javascript and HTML/ CSS. But this is not very exposed to the user, and web extensions are intentionally limited.
The modern browser engine exposes a lot of controls to scripts and to the chrome layer. IIRC Firefox uses this extensively to code (most of) the UI in Javascript and HTML/ CSS. But this is not very exposed to the user, and web extensions are intentionally limited.