On the example page there is an animated picture. It animates by changing the y position of the background image. If you inspect the element you'll notice nothing changing. The background-position is in-line and static. Now if you view it using FireBug in FF3/4 you'll notice on the dom tree view the inline style is constantly changing. This is useful for debugging. When I first viewed the page I wasn't able to determine what was happening in webkit, but could in FF.
*** Bug 52125 has been marked as a duplicate of this bug. ***
*** This bug has been marked as a duplicate of bug 44620 ***