It concerns a 2001 proposal to style scrollbars, which Firefox still doesn&#x27;t <i>want</i> to support to this day.
It&#x27;s 2016, we have web apps, but we have no way to change or hide the ugly Firefox scrollbars (assuming we don&#x27;t want to write our library to render custom scrollbars, which is inherently fragile and not trivial).