请问一个有关FireFox起始页面的问题

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<html xmlns="http://www.w3.org/1999/xhtml" lang="zh-Hans" xml:lang="zh-Hans">
    <head>
        <meta http-equiv="Content-Type" content="text/html;charset=utf-8" />
        <meta http-equiv="x-dns-prefetch-control" content="on" />
        <meta http-equiv="keywords" content="Mozilla, Mozilla Online, Firefox, Firefox China Edition, 火狐, 火狐中国版" />
        <meta http-equiv="X-UA-Compatible" content="chrome=1" />
        <title>火狐起始页</title>
        <link rel="dns-prefetch" href="http://google-analytics.com/" />        <script type="text/javascript" src="js/json2.js"></script>
        <link rel="stylesheet" type="text/css" href="css/style_z.css" />
        <!--[if IE]>
        <meta http-equiv="X-UA-Compatible" content="IE=8" />
        <link rel="stylesheet" type="text/css" href="css/style_z.ie.css" />
        <script id="__ie__" type="text/javascript" src="js/index.ie.js"></script>
        <![endif]-->
        <style type="text/css">
#zheader {width:681px; margin:60px auto 3px auto; background:#fff url(images/zbg.png) no-repeat 25px center; height:120px;}
#zlink {width:631px; margin:40px auto; text-align:center;}
#zlink a {margin:0 10px;}
.zsearch {width:629px; height:138px!important; margin:0 auto!important;}
.zsearch > form {height:90px!important; padding:43px 0 20px 10px!important;}
#zfooter {margin:0 auto; width:33em; font-size:85%; background:#fff url(images/logo_head.png) no-repeat left 4px; padding-left:50px;}
#zfooter p {margin:0; padding:0;}
        </style>
        <script type="text/javascript" src="js/index_z.js"></script>
    </head>
    <body>        <div id="zheader"></div>
        <div id="search" class="round-box zsearch">
            <ul onclick="SEARCH.change(event)">
                <li><a class="grad-box" href="http://www.google.cn/" title="谷歌搜索" rel="google_web">谷歌</a></li>
                <li><a class="current" href="http://www.baidu.com/index.php?tn=monline_5_dg" title="百度一下" rel="baidu_web">百度</a></li>
                <li><a class="grad-box" href="http%3A%2F%2Fadtaobao.allyes.cn%2Fmain%2Fadfclick%3Fdb%3Dadtaobao%26bid%3D10573%2C3476%2C805%26cid%3D36829%2C581%2C1%26sid%3D72694%26show%3Dignore%26url%3Dhttp%3A%2F%2Fs.click.alimama.com%2Fma_a%3Fne%3DtSIPNYxvJwgg%252BABaFJJT9yrjMpLs6u363fPiGsQmJhp8I7FL%252FLbH0Ekngc4hpoB9EnYik0vGAnvZ%252Bsy9ULReJ85b%252BDbFRT1lNrt95Zna3IHiVmRLPHiiuDqegZYfKbtNzztGhiVeFPrnDWRfwfBvDnwPJvnBcWhb" title="购物搜索" rel="taobao">淘宝</a></li>
                <li><a class="grad-box" href="http://www.google.cn/music" title="音乐搜索" rel="google_music">音乐</a></li>                <li><a class="grad-box" href="http://video.baidu.com/" title="视频搜索" rel="baidu_video">视频</a></li>
                <li><a class="grad-box" href="http://image.baidu.com/" title="图片搜索" rel="baidu_image">图片</a></li>
                <li><a class="grad-box" href="http://zhidao.baidu.com/" title="百度知道" rel="baidu_zhidao">知道</a></li>
                <li><a class="grad-box" href="http://ditu.google.cn/" title="地图搜索" rel="google_ditu">地图</a></li>
                <li><a class="grad-box" href="http://www.verycd.com" title="影视搜索" rel="verycd_movie">影视</a></li></ul>
            <form name="form1" method="get" onsubmit="return SEARCH.submitform(event);" action="/s" target="_blank">                <a href="" title="百度一下" rel="_blank" target="external"><img src="images/logo/baidu_web.png" alt="" /></a>
                <script type="text/javascript"><!--
google_ad_client = "pub-0676661022110159";
google_ad_format = "js_sdo";
google_searchbox_width = 420;
google_searchbox_height = 25;
google_link_target = 2;
google_ad_height = 26;
google_ad_width = 520;
//-->
                </script>
                <script type="text/javascript" src="http://pagead2.googlesyndication.com/pagead/show_sdo.js"></script>
                <iframe frameborder="0" scrolling="no" style="height:29px;" id="baidu_zhidao_frame" src="z_bdzd.html"></iframe>
                <iframe frameborder="0" scrolling="no" style="height:29px;" id="taobao_zhidao_frame" src="z_taobao.html"></iframe>
                <input type="text" id="q" />
                <input type="hidden" id="s" value="baidu_web" />                <button type="submit" class="round-box grad-box">百度一下</button>
            </form>
        </div>
        <script type="text/javascript">SEARCH.init();</script>
        <div id="zlink">
            <a href="http://addons.sociz.com/firefox" title="为Firefox添加新功能" target="_blank" rel="external">为Firefox添加新功能</a>
            <a href="http://www.mozillaonline.com/products/firefox/features/" title="了解更多Firefox特性" target="_blank" rel="external">了解更多Firefox特性</a>            <a href="http://g-fox.cn/bbs/" title="询问产品使用问题" target="_blank" rel="external">询问产品使用问题</a>
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这个是FireFox起始搜索页面的代码。我所不明白，想请教大家的问题的是 在点选调用的函数方法SEARCH.change(event)是写在哪个文件中的啊？json2.js这个文件中是没有的 有高手知道的帮助一下吧 谢谢了额