rem: var string = XPCU.QI(data, "nsISupportsWString"); 
add: var string = XPCU.QI(data, "nsISupportsString"); 
context:   onDragDropIn: function(aEvent)  {    var data = DNDUtils.getData("TreeBuilder/column-remove", 0);    var string = XPCU.QI(data, "nsISupportsWString");    this.addItem(string.data);  },
meta: 9421	/local1/tlutelli/issta_data/temp/all_js/javascript/2006_temp/2006/9421/3703f3c61bce0c45d03ff380dc6b806f944ecb73/columnsDialog.js/clean/extensions/inspector/resources/content/viewers/dom/columnsDialog.js