Css 3级导航菜单，适用ie和firefox

<style type="text/css">
/* 基本样式 */
.menur {font-family: arial, sans-serif; position:absolute; z-index:0;margin:0;left:0px;top:24px;   font-size:12px; margin:0px 1px;}
.menu {font-family: arial, sans-serif;   height:30px; position:absolute;z-index:1; margin:0;  font-size:12px; margin:0px 1px;}
.menu ul li a, .menu ul li a:visited {display:block;   text-decoration:none; color:#000; width:50px; height:25px; border:0px solid #e4e4e4; border-width:0px 0px 0px 0; line-height:22px; font-size:12px;}
.menu ul {padding:0; margin:0;list-style-type: none;}
.menu ul li {float:left; margin-right:1px; position:relative;}
.menu ul li ul {display: none;}
/* 指定非IE浏览器样式 */
.menu ul li:hover a {text-decoration: none; color:#000; background:#e4e4e4;}
.menu ul li:hover ul {text-decoration: none; display:block; position:absolute; top:24px; left:0px; width:105px;}
.menu ul li:hover ul li a.hide {text-decoration: none; background:#e4e4e4; color:#000;}
.menu ul li:hover ul li:hover a.hide {text-decoration: none; width:130px;}
.menu ul li:hover ul li ul {text-decoration: none; display: none;}
.menu ul li:hover ul li a {text-decoration: none; display:block;     background:#e4e4e4; color:#000; width:130px;}
.menu ul li:hover ul li a:hover {text-decoration: none; background:#f1f5ff; color:#0000cc;}
.menu ul li:hover ul li:hover ul {text-decoration: none; display:block;     position:absolute; left:130px; top:0; color:#000;}
.menu ul li:hover ul li:hover ul li a {text-decoration: none; display:block; width:150px; background:#e4e4e4; color:#000;}
.menu ul li:hover ul li:hover ul li a:hover {text-decoration: none; background:#f1f5ff; border:0px solid #e4e4e4; color:#0000cc;}
</style>
<!--[if lte IE 6]>
<style type="text/css">
/* 指定IE6 浏览器样式 */
table {border-collapse:collapse; border:0;   margin:0; padding:0;}
.menu ul li a.hide, .menu ul li a:visited.hide {text-decoration: none;   display:none;}
.menu ul li a:hover ul li a.hide {text-decoration: none; display:none;}
.menu ul li a:hover {color:#000; text-decorat