The Mozilla bug (referenced in the URL) was originally filed by David Hyatt and this is now fixed and will be included in the next version of Firefox. Implementing -webkit-image-rect would allow CSS spriting without introducing dummy DOM nodes.
See also http://www.w3.org/TR/css3-images / http://dev.w3.org/csswg/css3-images/
<rdar://problem/19103405>
Replaced by https://www.w3.org/TR/media-frags/#naming-space ?