IE和FireFox JavaScript 的兼容问题。。

function showHide(id)
{
  var el= document.getElementById(id);//?? <li>???id
  var bExpand = true;//???Action???
  var images = el.getElementsByTagName("img");//?? <li> </li>????? <IMG>??
  if (images[0].src.indexOf("minus.gif")!=-1)//?????????
  {
    bExpand = false;//??Action???
    images[0].src="images/images/plus.gif";//???????
  }else{
    images[0].src="images/images/minus.gif";//?????????
  }
  var subs=el.lastChild;//?? <ul> </ul>??
  if(bExpand)//?????
    subs.style.display="block";//?? <ul> </ul>?????
  else//?????
    subs.style.display="none";//?? <ul> </ul>?????
}

function getSubTree(id)
{
  var submitURL="treeview?parent="+id;
  postXmlHttp( submitURL, 'parseSubTree("'+id+'")' ,'load("'+id+'")');
}
function parseSubTree(id)
{
  var el= document.getElementById( id );//???id? <li>??
  var ulElmt= document.createElement("UL");//???? <ul>??
  ulElmt.innerHTML=_xmlHttpRequestObj.responseText;//??????? <ul>
  el.appendChild(ulEl