var btn = document.createElement('a');
btn.setAttribute('href', url);
btn.setAttribute('_target', 'blank'); // here I need something like _null or _void
btn.textContent = 'Find the item externally';
var ref = document.evaluate('/div[@class="seaarch-form"]/div[@class="submit_button"]', node, null, XPathResult.FIRST_ORDERED_NODE_TYPE, null);
var btnNode = node.insertBefore(btn, ref.singleNodeValue);
btnNode.addEventListener("click", search_external, false);
.
.
.
function search_external() {
  var url = this.href;
  //system('firefox ' + url); // not supported
}