GNOME Bugzilla – Bug 774263
Black borders in Firefox since Gtk 3.20
Last modified: 2016-11-12 16:04:26 UTC
Also the menu separators are black. See this Firefox bug report: https://bugzilla.mozilla.org/show_bug.cgi?id=1303964 And a work-around from reddit: https://www.reddit.com/r/gnome/comments/5c7x0u/how_to_fix_firefox_black_borders_in_gnome_320/ Is Firefox using some CSS attributes not available anymore in Gtk+ 3.20 and above?
The selector for separators changed in 3.20 from 'GtkSeparator' to 'separator'.
This really is a firefox bug, I don't want to have workarounds in the official gtk+ themes. I we do that the proper fixes will probably never lands.
I guess I know wassup there, that css basically sets the "color" prop and "fix" the theming so probably firefox look for the wrong properties, for example in 3.20 we don't set a "color" on separators as it was done previously, since now the separator is just a box, so it's styled using the background related properties, hence the "color" prop is inherited and doesn't make sense there. Something similar probably happens for frames, the relevant properties are the border related ones now on the frame border node.