var Err = "Boton derecho deshabilitado"; //A simple variable for holding Error Message

function disableRightClick(btnClick) //Function that will execute on right click
{
 if (navigator.appName == "Netscape" && btnClick.which == 3) // Netscape 
 {
  alert(Err);//Alert for display a message
  return false;
 }
 else if (navigator.appName =="Microsoft Internet Explorer" && event.button == 2)  // IE
 {
  alert(Err);
  return false;
 }
}
document.onmousedown = disableRightClick;