firefox中iframe改变父窗口url，document.write会失效？
两个页面,a.html:
<html>
<body>
<script> document.write( 'asdfasdfasfd ') </script>
<a href= "a.html " > go </a>
<iframe src= "b.html " width=400px height=300px > </iframe>
</body>
</html>
b.html:
<html>
<body>
<a href=a.html target=_top > go </a>
</body>
</html>
在IE中正常，firefox中会出现document has no properties的错误
[解决办法]
主所的情；