CSS3 transform has had support for skew() for quite awhile, allowing us to do cool things like rotate and manipulate objects that would otherwise just be boxes.

skew() has been replaced with skewX() and skewY() due to some confusion over how skew() works. That's fine - CSS3 is still a work in progress. But Firefox intentionally yanking support for such a major feature, that large portions of the internet rely on, seems like a very shortsighted decision to me.

Interesting fact: css3generator.com is now broken on Firefox due to this.