Ambiance : odd vertical padding in Firefox 60 with no title bar

[Francois Thirioux]

I run Firefox 60 in Ubuntu 18.04 without window title bar (new option). The extra space option to grab the window does not change anything.

There is no issue with Adwaita or Communitheme. In Ambiance (see screenshot), there is a rather big vertical padding above the tabs ; thus the close button is vertically centered in the header bar but does not fit with the tabs/icons line.