It's also a fun bit of "everything old is new again". The scrollbar color CSS this points out for Firefox originated somewhere in IE 3-6 when Windows 9X was briefly encouraging fun with scrollbar colors to better match content and there was a lot of applications that did so on Windows (it was the early WinAMP, Napster, etc era). Other platforms complained about how "tacky" such CSS was, and by the time Firefox implemented it most people thought it was a bad idea of the BLINK/MARQUEE school. It's almost strange this time to see it from the other direction of macOS web devs wanting more Mac-like scroll bars everywhere.