There are no real improvements coming to Firefox Nightly on Android. All the real action is happening in Firefox Focus with GeckoView: https://github.com/mozilla-mobile/focus-android/wiki/Release... and in Fenix: https://github.com/mozilla-mobile/fenix

Fennec (Firefox for Android) is basically in maintenance mode.

FWIW: Firefox Focus Nightly is a much better implementation of Gecko on Android than Fennec ever was, with the caveat that Sync, sessions, or extensions are not available.