As noted in bug 1236506 and bug 605985, "-moz-appearance:none" doesn't really work the same way "-webkit-appearance:none" does (at least, not for checkboxes & radio buttons). So, for sites that are conscientious and use feature-detection to sniff for "-webkit-appearance" support (and provide fallback when it's not), our current aliasing behavior (on Nightly) moves us from working fallback code to not-working -webkit-appearance dependent code. (where "not working" means "checkbox maybe still shows up but it looks out of place because it's not themed like the rest of the site") This is a usability regression. See screenshots on bug 1236506 for an example of this. We should probably hold off on shipping "-webkit-appearance" as an alias, at least until we've got a better plan for bug 605985.

I believe this particular alias wasn't actually buying us too much in terms of site-fixing, which is why I'm not too concerned with removing it. I think Mike is on board with removing it, too, per bug 605985 comment 42 ("We should probably consider removing the -webkit-appearance alias until we understand all the issues (and ideally match on behavior).")

Thanks! Sanity-check Try run: https://treeherder.mozilla.org/#/jobs?repo=try&revision=418464266496

Yep, I think the differences between -moz- and -webkit- are too big for an alias to get us much. Expect bugs to follow once we have a better understanding of how people are using this in the wild (akin to Bug 605985).

Is there already a bug for reimplementing -webkit-appearance once bug 605985 is fixed? Sebastian

Not that I'm aware of. I filed bug 1302104 on that.