在Firefox浏览器里为何不能调用js,而在ie里却可以？？？？？

Question

<script type="text/javascript">
function popup(popwin)
         {
  closepopwin('popwin_setmtag');
  closepopwin('popwin_newmtag');
   showpopwin(popwin);
         } </script>
<form method="post" action="space.php?do=group">
<p style="text-align:center; line-height: 22px;">$_SN[$_SGLOBAL[supe_uid]] 已登陆
                 
    <select name="mygroup" style="width:138px;" onchange="a(this.options[selectedIndex].value)" class="textinput">
<option value="" selected="selected">我加入的群组</option>
<!--{if !Empty($mymtag2)}--><!--{loop $mymtag2 $value}-->
<option value="space.php?do=mymtag&view=thread&tagid={$value[tagid]}">$value[tagname]</option>
<!--{/loop}--><!--{/if}--> 
</select>
      </p> <p style="text-align:center; line-height: 22px;">
<input type="text" name="tagname" value="" class="t_input" size="11" />
<input type="submit" name="findsubmit_btn" value="找群" class="submit" />
</p>
<p style="text-align:center; line-height: 22px;">
<!--<a href="#">退出</a><span class="pipe">|</span>  -->
   <span><a href="javascript:popup('popwin_setmtag');">群设置</a></span><span class="pipe">|</span>
<a href="javascript:popup('popwin_newmtag');">创建群</a>
                    
<input type="hidden" name="formhash" value="<!--{eval echo formhash();}-->"/>
</p>
</form>//弹出窗口
function showpopwin(wndName)
{
//visibility: visible;
if(document.getElementById(wndName).style.visibility!="visible"){
var myobj=document.getElementById(wndName);
var bodyhh=window.screen.availHeight;
var bodyww=window.screen.availWidth;
var objhh=myobj.clientHeight;
var objww=myobj.clientWidth;
var T = document.documentElement.scrollTop;
var L = document.documentElement.scrollLeft;

myobj.style.left       = (bodyww-objww)/2 + L;
myobj.style.top        = (bodyhh-objhh)/2 + T;
myobj.style.visibility = "visible";
}
}