Do setDragImage or addElement work?

i've tried to set a drag image according to the doc
https://developer.mozilla.org/En/DragDrop/Drag_Operations#dragfeedback

as well as usage in mozilla-central codebase (all of 2), for which 
neither the favicon drag image when dragging 1) the urlbar identity box, 
nor 2) a tab, actually work.

i haven't found any working example in html5, using Fx 9a, either.  can 
anyone verify if this is indeed supported, as the docs seems to 
indicate, and if there is an example anywhere?