js在firefox出错，在firefox中不能自动点击

<a id='aRefer' href='http://www.' target='_self'>网易</a>
<script language='javascript'>
    if(navigator.userAgent.indexOf("MSIE")>0){
    document.getElementById('aRefer').click();
   
    }else{
        var   a=document.createEvent("MouseEvents");
        a.initEvent("click",   true,   true);  
        document.getElementById('aRefer').dispatchEvent(a);
    }
</script>