<SCRIPT language=JavaScript>
<!– http://www.spacegun.co.uk –>
 var message = “function disabled”;
 function rtclickcheck(keyp){ if (navigator.appName == “Netscape” && keyp.which == 3){  alert(message); return false; }
 if (navigator.appVersion.indexOf(“MSIE”) != -1 && event.button == 2) {  alert(message);  return false; } }
 document.onmousedown = rtclickcheck;
</SCRIPT>
 
or this one
 
 <script>
var isNS = (navigator.appName == "Netscape") ? 1 : 0;
  if(navigator.appName == "Netscape") document.captureEvents(Event.MOUSEDOWN||Event.MOUSEUP);
  function mischandler(){
   return false;
}
  function mousehandler(e){
var myevent = (isNS) ? e : event;
var eventbutton = (isNS) ? myevent.which : myevent.button;
    if((eventbutton==2)||(eventbutton==3)) return false;
}
document.oncontextmenu = mischandler;
document.onmousedown = mousehandler;
document.onmouseup = mousehandler;
  </script>
