$(elem).css('backgroundPositionY')
does it on chrome, ie, and safari, but not Firefox (nor Opera I believe). You'd think jQuery would have a polyfill but it doesn't, as of 1.5. How can I easily get the background Y position for e.g. background animations (for e.g. parallax)?
EDIT: Tell Mozilla you want background-position-[x,y] support. (use the "vote" feature, not comment, unless you have something prescient to add). Bug has been open since 2010 tho (3 years now) so don't hold your breath for a fix. :)