Private window consistencies

[julianfairfax]

Describe the bug As of https://github.com/lassekongo83/adw-gtk3/commit/ab007022239bad400d555acf2f1755fac328eba9, adw-gtk3 has been updated to not override GNOME Web's private window titlebar colour. As with the Adwaita theme, GNOME Web with the adw-gtk3 theme now has a blue titlebar in private windows. However, Firefox GNOME theme applies this blue to the whole private window, as opposed to just the titlebar. In my opinion, this should be changed to be consistent with GNOME Web.

To Reproduce

1. Open a private window
2. Observe

Expected behavior Only the window titlebar should be blue.

Screenshots GNOME Web GTK3:

GNOME Web with adw-gtk3:

Firefox with Firefox GNOME theme:

Setup information

• OS: Arch Linux
• Installation method: Flatpak
• Firefox version: 110
• Theme version: master
• Optional features enabled: gnomeTheme.bookmarksToolbarUnderTabs, gnomeTheme.hideSingleTab

[julianfairfax]

This shouldn't be hard to fix?