I'm pretty sure you are all familiar with the adwaita-firefox  theme.
It makes Firefox looks more "native" on GNOME, thus making the user
experience more consistent.
I suggest we package it and make it default for the desktop spin. This
1) Packaging the theme itself
2) Make firefox use it by default (example from Suse )
3) Make sure we don't update Firefox without the theme being updated as well
I think this would be a noticeable improvement in user experience.