如何在firefox中实现style.pixelTop和style.pixelLeft _JavaScript

怎么在firefox中实现style.pixelTop和style.pixelLeft

document.oncontextmenu=function() {

mlay.style.display="";
mlay.style.pixelTop=event.clientY;
mlay.style.pixelLeft=event.clientX;
return false;
}

这是一个发生右键事件时来控制一个DIV
<div id="mlay" style="position: absolute; display: none; cursor: default;"onClick="return false;"></div>

带代码只在ie中有效，请问怎么能兼容firefox呢？

------解决方案--------------------

HTML code

<div id="mlay" style="position: absolute; display: none; cursor: default;"onClick="return false;">菜单</div>
<script type="text/javascript">

    document.oncontextmenu = function (event) {
        var mlay = document.getElementById('mlay');
        mlay.style.display = "";
        event = event || window.event;
        mlay.style.top = event.clientY + 'px';
        mlay.style.left = event.clientX + 'px';
        return false;
    }  </script>