iframe加载时的loading效果，兼容Firefox

 <head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312">
<title>新建网页 1</title>
</head>
<body>   
<div align="center" style="position: absolute; width: 100px; height: 100px; z-index: 1; left:158px; top:17px"  /> loading...</div>
<iframe style="visibility:hidden" onreadystatechange=stateChangeIE(this) onload=stateChangeFirefox(this) name="callframe" ></iframe>
<script>   
    function stateChangeIE(_frame)
    { 
     if (_frame.readyState=="interactive")//state: loading ,interactive,   complete
     {
     var loader = document.getElementById("load"); 
        loader.innerHTML      = "";    
        loader.style.display = "none";  
        _frame.style.visibility = "visible";   
     }   
    }
    function stateChangeFirefox(_frame)
    { 
     var loader = document.getElementById("load"); 
        loader.innerHTML      = "";    
        loader.style.display = "none";  
        _frame.style.visibility = "visible";   
    }
    callframe.location.href="http://www.hao123.com"; 
</script>   
</body>
</html>
摘自：http://blog.csdn.net/sgear/article/details/2862397