firefox-gui-chrome-css/chrome/userChrome.css

var(--toolbar-bgcolor, #2a2e32);

:root:not([inFullscreen]) #a11y-announcement {
	/* Kludge to make "a11y-announcement" a replacement for the removed "browser-bottombox" element */
	display: block !important;
	/* Also give it the right colour - and Mozilla says "opaque for layers optimization" (although this may not apply) */
	background-color: var(--toolbar-bgcolor) !important;
}
#browser-bottombox, 
#a11y-announcement {
	height: 20px;
	border-top: solid 1px #505050;
}
#statuspanel {
	position: fixed !important;
	height: 20px !important;
	width: 100% !important;
	left: 0px !important;
	bottom: 0px !important;
	padding: 0px !important;
	transition-duration: 0s !important;
	transition-delay: 0s !important;
	transition-property: none !important;
}
#statuspanel>* {
	color: var(--toolbar-color) !important;
	background: transparent !important;
	border: none !important;
}

html[inFullscreen="true"] #browser-bottombox, 
html[inFullscreen="true"] #a11y-announcement {
	display:none !important;
}
/* Make status text visible - as a pop-up box */
html[inFullscreen="true"] #statuspanel>* {
	border: 1px solid #505050 !important;
	padding-left: 2px !important;
	padding-bottom: 6px !important;
	background: var(--toolbar-bgcolor) !important;
}