Firefox with CSD (Client Side Decorator) has useless border around window - in maximized window!
In GNOME Shell no has this border. In Cinnamon has.
Other program do not have this border neither on the GNOME Shell nor on the Cinnamon.
Problem is in Firefox + CSD + Cinnamon.
I use Antergos(Arch) + Cinnamon.
It is ugly and interferes with selecting tabs and scrolling with the scroll bar.
How hide this border?