Comment 18 for bug 1871644

Emilio, you're absolutely right :) There's original Bug 1408360 for it.

For custom themes we need to apply alpha component only and keep original color from theme (i.e. paint over alpha from theme).

Emilio, how is the best way how to do it? We can introduce a new appearance (-moz-window-titlebar-alpha for instance) which contains only alpha component from titlebar and paint it over theme color or use existing one (-moz-window-titlebar) but I'm not very experienced in js/css styling so I'll appreciate any help here.