The previous page works as expected. This one, though adds position:fixed to the Draggable div and has the following problem in Firefox: If you drag without scrolling, everything works as expected. Go ahead and try it. Then refresh. If you now scroll the page a bit, though, shadow that follows the mouse when dragging is not aligned with the mouse pointer; it's above it somewhere, an amount determined by the scroll. In my actual environment, this is also happening in IE, but there is much more going on there related to the position:fixed section, which I haven't yet isolated.