Firefox restyled Linux menupopups at some point to no longer conform to
the DE defined styles for GTK widgets. This removes that custom firefox
styling and uses DE defined values instead. This is especially apparent
on Linux Unity where menupopups are dark in both light and dark themes
by default for apps.
Reasoning:
- Different Linux DEs specify different titlebar button (min, max,
close) locations which we did not and could not support before.
- Previous approach copied from Firefox depended on custom offsets
specified in CSS instead of allowing the browser engine to place
elements
Changes:
- Titlebar and menubar no longer collapsed into each other with a
negative margin, instead just a single flexbox (on macOS the titlebar
is still collapsed into the tab bar)
- Support for -moz-gtk-csd-reversed-placement to correctly place the
titlebar buttons on Linux
- Removed/changed some code copied from Firefox that does not apply or
uses the wrong selectors
- Fixed the display of Linux Unity DE buttons with icons appearing outside
of button borders
- Removed the Z in the titlebar on Linux since only a few DEs use that.
- Aligned the tabbar on Linux and Windows to the left margin of the
window.
