div height problem

div height problem


a div has a style of "height:65%;overflow:scroll" ,but it doesn't
work in firefox.(it's ok in ie)
who can help me?
the source code as following:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://
www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<style type="text/css">
<!--
.gabby{
    font-size: 10px;
    font-family: Verdana,Arial,Helvetica,sans-serif;
}
a:link,a:active,a:visited {
    text-decoration: none;
}
.gabby_top {
    margin: 1px;
    height: 20px;
    width: 100%;
}
.gabby_content {
    white-space:normal;
    word-break:break-all;
    overflow: scroll;
    overflow-x:hidden;
    height: 65%;
    width: 100%;
    background-color: #FFFFFF;
    margin-bottom: 5px;
}
.gabby_bottom {
    height: 20%;
    bottom: 2px;
}
.gabby_status {
    color: #CCCCCC;
}
.gabby_user{
    border: 1px solid #b3b3b3;
    height: 20px;
    margin: 2px;
}
.gabby_input{
    overflow:auto;
    width: 80%;
    height: 30px;
}
-->
</style>
<link rel="stylesheet" href="../themes/flora/flora.all.css" type="text/
css" media="screen" title="flora (Default)">
<script language="javascript" src="../jquery.js"></script>
<script type="text/javascript" src="../jquery.dimensions.js"></script>
<script type="text/javascript" src="../ui.mouse.js"></script>
<script type="text/javascript" src="../ui.draggable.js"></script>
<script type="text/javascript" src="../ui.accordion.js"></script>
<script type="text/javascript" src="../ui.resizable.js"></script>
<script type="text/javascript" src="../ui.dialog.js"></script>
<script type="text/javascript">
var url = '{{url}}';
var comments_num = 0;
var user_color={};
var
color=["#FF0000","#00FF00","#0000FF","#000000","#00FFFF","#FF00FF"];
var comment="";
$(document).ready(function(){
    $.ajaxSetup({
        async: false,
        cache:false
    });
    setInterval("get_comments()", 3000);
    $("#gabby").dialog(
    {height:350,
     width:350,
     minWidth:350,
     minHeight:350,
     position:'rightbottom',
     resize:true,
     title:"Chat"
    }
    );
});
function get_comments() {
    $(".gabby_content").prepend("<span style=\"color:"+"#FF0000"+ "\">"
            +"<a href='/user/"+"1"+"/' target='_blank'>"+"guest"+"</
a>:&nbsp;&nbsp;"+"hello world"+"</span>
");
    a={'url':url,'comments_num':comments_num};
}
function rand_color(){
    return color[Math.floor(Math.random()*6)];
}
function post_comment(){
    if(comment == $("#content").val()){
        $(".gabby_status").text("NO repeat!");
        return;
    }
    comment = $("#content").val()
    a={'url':url,'object':0,'ajax':1};
    a['creator']=$("#creator").val();
    a['content']=$("#content").val();
    $.ajax({
        type:"POST",
        url:'/topic/add_comment/',
        data:a,
        success:function(data) {
            $(".gabby_status").text("sucessful！");
        },
        error:function(data){
            $(".gabby_status").text("failed！");
        }
    }
    );
}
</script>
<title>Gabbly </title>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" /></
head>
<body>
<!--<div >
<iframe src="{{url}}" width="100%" height="100%" frameborder="0"
hspace="0" vspace="0" marginheight="0" marginwidth="0"></iframe>
</div> -->
<div id='gabby' class="flora">
    <div class='gabby_top'>
        <div style="float: left;">
        <img src="/site_media/image/watched_n.gif" />
        <!--{% if user.is_anonymous or not user %}
         <input id="creator" type="text" value="Guest" size="8"
class="gabby_user">
         {% else %}
         <input id="creator" type="text" value="{{ user.username }}"
size="8" class="gabby_user">
         {% endif %} -->
         <span class='gabby_online'></span>
        </div>
        <div style="float:right"><a href="/user/login">登录</a>|<a href="/user/
register">注册</a></div>
        <div style="clear:both"></div>
    </div>
    <div class='gabby_content'>
    </div>
    <div class='gabby_bottom'>
        <span class='gabby_status'></span>
        <textarea id="content" class="gabby_input"></textarea><br />
        <input type="submit" value="发送" onClick="post_comment()">
    </div>
</div>
</body>
</html>