function right(e) {
   var msg = "Sorry, you don't have permission to right-click.";
   if (navigator.appName == 'Netscape' && e.which == 3) {
     alert(msg);  // Delete this line to disable but not alert user
     return false;
   }
   else
   if (navigator.appName == 'Microsoft Internet Explorer' && event.button==2) {
     //alert(msg); // Delete this line to disable but not alert user
     return false;
   }
   return true;
}

document.onmousedown = right;