The CSS 2D Transforms and 3D Transforms mod­ules have been merged into a single mod­ule: CSS Transforms. The only prac­tical change this has res­ul­ted in so far is the removal of the skew() func­tion — skewX() and skewY() remain unchanged.

The -moz-skew() func­tion has been removed from Firefox 14, and Example 12–05 has been updated to show this.

— 25 June, 2012