/*
if (window.Event) 
document.captureEvents(Event.MOUSEUP); 

function nocontextmenu() 
{ 
event.cancelBubble = true 
event.returnValue = false; 

return false; 
} 

function norightclick(e) 
{ 
if (window.Event) 
{ 
if (e.which == 2 || e.which == 3) 
return false; 
} 
else 
if (event.button == 2 || event.button == 3) 
{ 
event.cancelBubble = true 
event.returnValue = false; 
return false; 
} 

} 
if (document.layers) { 
document.captureEvents(Event.MOUSEDOWN); 
} 
document.oncontextmenu = nocontextmenu; 
document.onmousedown = norightclick; 
document.onmouseup = norightclick; 
//--> 

*/
<!--- Inicio do script de desabilitar botao no FireFox-->
function mouseDown(e) {
var shiftPressed=0;
var ctrlPressed=0;
if (parseInt(navigator.appVersion)>3) {

  if (navigator.appName=="Mozilla")
       shiftPressed=(e.modifiers-0>3);
  else shiftPressed=event.shiftKey;

  if (navigator.appName=="Mozilla")
       ctrlPressed=(e.modifiers-0>1);
  else ctrlPressed=event.ctrlKey;

  if (shiftPressed || ctrlPressed) {
   alert ('Opção desativada. Agradecemos sua compreensão.');
   return false;
  }

}
return true;
}

if (parseInt(navigator.appVersion)>3) {
document.onmousedown = mouseDown;
   if (navigator.appName=="Netscape")
     document.captureEvents(Event.MOUSEDOWN);
}
document.oncontextmenu=new Function("return false;");

function Verificar()
{
var ctrl=window.event.ctrlKey;
var tecla=window.event.keyCode;
	if (ctrl && tecla==67) {event.keyCode=0; event.returnValue=false;}
	if (ctrl && tecla==86) {event.keyCode=0; event.returnValue=false;}
}