var isNS = (navigator.appName == "Netscape") ? 1 : 0;

if (navigator.appName == "Netscape") document.captureEvents(Event.MOUSEDOWN || Event.MOUSEUP);

function mischandler() { return false; }
function mousehandler(e) {
    var myevent = (isNS) ? e : event; var eventbutton = (isNS) ? myevent.which : myevent.button;
    if ((eventbutton == 2) || (eventbutton == 3)) return false;
}
document.oncontextmenu = mischandler;
document.onmousedown = mousehandler;
document.onmouseup = mousehandler;