add:  if (node.getAttribute('folder') == 'true') { continue; } 
context: function PreviewPanel() {  var tree = document.getElementById('other-panels');  var database = tree.database;  var select_list = tree.selectedItems  for (var nodeIndex=0; nodeIndex<select_list.length; nodeIndex++) {    var node = select_list[nodeIndex];    if (!node)    break;    var id = node.getAttribute("id");    if (!id)      break;    var rdfNode = RDF.GetResource(id);    if (!rdfNode) break;    var preview_name = getAttr(database, rdfNode, 'title');    var preview_URL  = getAttr(database, rdfNode, 'content');    if (!preview_URL || !preview_name) break;    var preview = window.open("chrome://sidebar/content/preview.xul",                              "_blank", "chrome");    preview.panel_name = preview_name;    preview.panel_URL = preview_URL;  }}
meta: 10234	/local1/tlutelli/issta_data/temp/all_js/javascript/2006_temp/2006/10234/1a32cc1c526c53fd9e341d35b5639757bb33402a/customize.js/buggy/suite/common/sidebar/customize.js