rem: AddAttachment(aData, prettyName); 
add: if (!(DuplicateFileCheck(aData))) AddAttachment(aData, prettyName); else { dump("###ERROR ADDING DUPLICATE FILE \n"); var errorTitle = Bundle.GetStringFromName("DuplicateFileErrorDlogTitle"); var errorMsg = Bundle.GetStringFromName("DuplicateFileErrorDlogMessage");  if (commonDialogsService) commonDialogsService.Alert(window, errorTitle, errorMsg); else window.alert(errorMsg); }   
context:   onDrop: function (aEvent, aData, aDragSession)    {      aData = aData.length ? aData[0] : aData;      if (aData.flavour == "text/x-moz-url" || aData.flavour == "text/nsmessage") {          aData = aData.data.data.toString();          // pull out the URL / title                    var prettyName;          var separator = aData.indexOf("\n");          if (separator != -1) {              prettyName = aData.substr(separator+1);              aData = aData.substr(0,separator);          }          AddAttachment(aData, prettyName);      }    },
meta: 10234	/local1/tlutelli/issta_data/temp/all_js/javascript/2006_temp/2006/10234/a77655ca07b815fe6faeca4f71c880a8b92e675c/MsgComposeCommands.js/clean/mailnews/compose/resources/content/MsgComposeCommands.js