in the example at the url: http://jsfiddle.net/VPTmA/2/ the filter is clipped in chrome, but not in firefox. given the filter width there should be no clipping in chrome and you should see the blur extend beyond the box. Note: resizing the page apparently triggers a redraw that shows things correctly extending beyond the clipped area.
Chrome and Firefox seem to handle this properly. Safari does not.
<rdar://problem/97098020>