public bool IsStyleSheetRegistered(string sheetURI, uint type)
        {
            nsIIOService ios = Xpcom.GetService <nsIIOService>("@mozilla.org/network/io-service;1");

            ios = Xpcom.QueryInterface <nsIIOService>(ios);
            nsIURI ssURI = ios.NewURI(new nsAUTF8String(sheetURI), null, null);

            if (!StyleSheetService.sheetRegistered(ssURI, type))
            {
                return(false);
            }
            return(true);
        }