virker ikke i netscape

hvorfor virker denne kode ikke i netscape ?:

<SCRIPT language="JavaScript">
function musA() {
  var targetId, srcElement, targetElement ;
  el = window.event.srcElement;
  if (el.className == "Outline") {
    targetId = el.id + "d";
    targetElement = document.all(targetId) ;
    if (targetElement.style.display == "none") {
        targetElement.style.display = "" ;
        el.src = "images/minus.gif" ;
    } else {
        targetElement.style.display = "none" ;
        el.src = "images/pluss.gif" ;
    }
  }
}

function clicka() {
  var targetId, srcElement, targetElement ;
  el = window.event.srcElement;
  if (el.className == "Outline") {
    targetId = el.id + "d";
    targetElement = document.all(targetId) ;
    if (targetElement.style.display == "none") {
        targetElement.style.display = "" ;
        el.src = "images/minus.gif" ;
    } else {
        targetElement.style.display = "none" ;
        el.src = "images/pluss.gif" ;
    }
  }
}

document.onclick = clicka ;
document.onmouseover = musA ;
</script>