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: 10234	/local1/tlutelli/issta_data/temp/all_js/javascript/2006_temp/2006/10234/f7ad4265ef6a40ea01c54009718ef28974e67fe9/columnsDialog.js/clean/extensions/inspector/resources/content/viewers/dom/columnsDialog.js