I didn’t think about appearance. But I wouldn’t actually count that one specifically, due to major cross-browser inconsistency, and the fact that -webkit-appearance is the form that all the browsers are now implementing—yes, under that name. (And the fancier parts of -moz-appearance are steadily being dismantled.) It’s the sort of thing that you write carefully in static CSS, rather than interacting with it in JavaScript. So to be absolutely clear: I would consider naive auto-prefixing of `appearance` to be very undesirable.

No new properties are being prefixed; that technique is dead, and the only things prefixed are so for historical reasons.