The chrome registry implements this interface to give overlays
 to the gecko XUL engine.
[scriptable, uuid(1d5b5b94-dc47-4050-93b7-ac092e383cad)]
interface nsIXULOverlayProvider : nsISupports

Methods

 Get the style overlays for a particular chrome URI.

 @param aURI  The URI being loaded
 @return      An enumerator of nsIURI for the overlays of this URI
nsISimpleEnumerator getStyleOverlays(in nsIURI aURI) 
 Get the XUL overlays for a particular chrome URI.

 @param aURI  The URI being loaded
 @return      An enumerator of nsIURI for the overlays of this URI
nsISimpleEnumerator getXULOverlays(in nsIURI aURI)