firefox-gnome-theme/chrome/theme.css

@import "parts/toolbox.css";
@import "parts/headerbar.css";
@import "parts/csd.css";
@import "parts/popups.css";
@import "parts/tabsbar.css";
@import "parts/remove-white-flash.css";
@import "parts/custom-icons.css";
@namespace xul "http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul";

:root {
    --space-above-tabbar: 0 !important;
}
#main-window {
	-moz-appearance: -moz-window-titlebar !important;
	background: none !important;
}

/* Sidebar */
#search-box {
	box-shadow: var(--gnome-urlbar-box-shadow) !important;
	height: var(--gnome-urlbar-height);
}