jQuery backgroundPosition conditional statement

I have this here:

if($("a#type").css('backgroundPosition') == '0px -40px')
//do something

Which passes fine in Ch开发者_如何学编程rome/Safari but not in Firefox 4. Is this a bug in jQuery? Has anyone else come across this? Is there a solution?

I think the syntax is like this:

if($("a#type").css('background-position') == '0px -40px')