function click() {
if (event.button==2||event.button==3) {
oncontextmenu='return false';
}
}
document.onmousedown=click
document.oncontextmenu = new Function("return false;")

<script language='Javascript'> 
function bloquear(e){return false} 
function desbloquear(){return true} 
document.onselectstart=new Function (&quot;return false&quot;) 
if (window.sidebar){document.onmousedown=bloquear 
document.onclick=desbloquear} 
</script>