mootools/mootools-core — pull request #2554 by SergioCrisostomo (2014-01-23 20:05:41+00:00)
Title: Antecipated backgroundPosition check

When element has no `background-position` values or after this happens in the testing:
`element.setStyle('background-position', null);`

Then inside getStyle:

var result = this.style[property]; // gives ""
if (!result || property == 'zIndex'){ //gives true from !result

So it goes inside the `if` and calls `result = this.getComputedStyle(property);`
which is in FF `"0% 0%"`

So by changing the order here I think it might kill the FF bug for
`'background-position'`