function inhabilitar(){
    return false 
} 
document.oncontextmenu=inhabilitar 
// IE
document.onselectstart=function(){
if(event.srcElement.type != "text" && event.srcElement.type != "textarea" && event.srcElement.type != "password")
return false
else return true;
};
// FIREFOX
if (window.sidebar){
document.onmousedown=function(e){
var obj=e.target;
if (obj.tagName.toUpperCase() == "INPUT" || obj.tagName.toUpperCase() == "TEXTAREA" || obj.tagName.toUpperCase() == "PASSWORD")
return true;
else if (obj.tagName=="BUTTON"){
return true;
}
else
return false;
}
}