<div id="curtain" style="position:absolute;top:10px;left:10px;100%;height:100%;bottom:0;z-index:0;-moz-opacity:0.5;background:gray;display:none;filter:alpha(opacity=50);">
<iframe src="javascript:false" style="position:absolute; visibility:inherit; top:0px; left:0px; 100%; height:100%; z-index:-1; filter='progid:DXImageTransform.Microsoft.Alpha(style=0,opacity=0)';"></iframe>
</div>
原理很簡單，利用 iframe 去蓋住。