css下拉列表在FF 20.0.1中不起作用

Question

我正在使用css创建一个下拉菜单。这在谷歌浏览器V26，IE9，Safari v 5.1.7中完美运行，但它在FF v20.0.1中根本不起作用。我想知道是否有人对我有任何提示或提示。对我来说，它的基本CSS，所以它应该在FF中正常工作。任何想法或有用的提示将不胜感激。谢谢你。

#cssmenu ul,
#cssmenu li,
#cssmenu span,
#cssmenu a {
  margin: 0;
  padding: 0;
  position: relative;
}
#cssmenu {
  height: 49px;
  border-radius: 5px 5px 0 0;
  -moz-border-radius: 5px 5px 0 0;
  -webkit-border-radius: 5px 5px 0 0;
  background: #141414;
      background:url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAAxCAIAAACUDVRzAAAAA3NCSVQICAjb4U/gAAAALElEQVQImWMwMrJi+v//PxMDw3+m//8ZoPR/qBgDEhuXGLoeYswhXg8R5gAAdVpfoJ3dB5oAAAAASUVORK5CYII=) 100% 100%; 
  background: -moz-linear-gradient(top, #32323a 0%, #141414 100%);
  background: -webkit-gradient(linear, left top, left bottom, color-stop(0%, #32323a),     color-stop(100%, #141414));
  background: -webkit-linear-gradient(top, #32323a 0%, #141414 100%);
  background: -o-linear-gradient(top, #32323a 0%, #141414 100%);
  background: -ms-linear-gradient(top, #32323a 0%, #141414 100%);
  background: linear-gradient(to bottom, #32323a 0%, #141414 100%);
  border-bottom: 2px solid #f1f1f1;
}
#cssmenu:after,
#cssmenu ul:after {
  content: '';
  display: block;
  clear: both;
}
#cssmenu a {
  background: #141414;
  background:url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAAxCAIAAACUDVRzAAAAA3NCSVQICAjb4U/gAAAALElEQVQImWMwMrJi+v//PxMDw3+m//8ZoPR/qBgDEhuXGLoeYswhXg8R5gAAdVpfoJ3dB5oAAAAASUVORK5CYII=) 100% 100%; 
  background: -moz-linear-gradient(top, #32323a 0%, #141414 100%);
  background: -webkit-gradient(linear, left top, left bottom, color-stop(0%, #32323a),     color-stop(100%, #141414));
  background: -webkit-linear-gradient(top, #32323a 0%, #141414 100%);
  background: -o-linear-gradient(top, #32323a 0%, #141414 100%);
  background: -ms-linear-gradient(top, #32323a 0%, #141414 100%);
  background: linear-gradient(to bottom, #32323a 0%, #141414 100%);
  color: #ffffff;
  display: inline-block;
  font-family: Helvetica, Arial, Verdana, sans-serif;
  font-size: 12px;
  line-height: 49px;
  padding: 0 20px;
  text-decoration: none;
}
#cssmenu ul {
  list-style: none;
}
#cssmenu > ul {
  float: left;
}
#cssmenu > ul > li {
  float: left;
}
#cssmenu > ul > li:hover:after {
  content: '';
  display: block;
  width: 0;
  height: 0;
  position: absolute;
  left: 50%;
  bottom: 0;
  border-left: 10px solid transparent;
  border-right: 10px solid transparent;
  border-bottom: 10px solid #f1f1f1;
  margin-left: -10px;
}
#cssmenu > ul > li:first-child > a {
  border-radius: 5px 0 0 0;
  -moz-border-radius: 5px 0 0 0;
  -webkit-border-radius: 5px 0 0 0;
}
#cssmenu > ul > li:last-child > a {
  border-radius: 0 5px 0 0;
  -moz-border-radius: 0 5px 0 0;
  -webkit-border-radius: 0 5px 0 0;
}
#cssmenu > ul > li.active > a {
  box-shadow: inset 0 0 3px #000000;
  -moz-box-shadow: inset 0 0 3px #000000;
  -webkit-box-shadow: inset 0 0 3px #000000;
  background: #070707;
  background:url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAAxCAIAAACUDVRzAAAAA3NCSVQICAjb4U/gAAAALklEQVQImWNQU9Nh+v//PxMDw3+m//8ZkNj/mRgYIHxy5f//Z0BSi18e2TwS5QG4MGB54HL+mAAAAABJRU5ErkJggg==) 100% 100%; 
  background: -moz-linear-gradient(top, #26262c 0%, #070707 100%);
  background: -webkit-gradient(linear, left top, left bottom, color-stop(0%, #26262c),     color-stop(100%, #070707));
  background: -webkit-linear-gradient(top, #26262c 0%, #070707 100%);
  background: -o-linear-gradient(top, #26262c 0%, #070707 100%);
  background: -ms-linear-gradient(top, #26262c 0%, #070707 100%);
  background: linear-gradient(to bottom, #26262c 0%, #070707 100%);
}
#cssmenu > ul > li:hover > a {
  background: #070707;
  background:url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAAxCAIAAACUDVRzAAAAA3NCSVQICAjb4U/gAAAALklEQVQImWNQU9Nh+v//PxMDw3+m//8ZkNj/mRgYIHxy5f//Z0BSi18e2TwS5QG4MGB54HL+mAAAAABJRU5ErkJggg==) 100% 100%; 
  background: -moz-linear-gradient(top, #26262c 0%, #070707 100%);
  background: -webkit-gradient(linear, left top, left bottom, color-stop(0%, #26262c),     color-stop(100%, #070707));
  background: -webkit-linear-gradient(top, #26262c 0%, #070707 100%);
  background: -o-linear-gradient(top, #26262c 0%, #070707 100%);
  background: -ms-linear-gradient(top, #26262c 0%, #070707 100%);
  background: linear-gradient(to bottom, #26262c 0%, #070707 100%);
  box-shadow: inset 0 0 3px #000000;
  -moz-box-shadow: inset 0 0 3px #000000;
  -webkit-box-shadow: inset 0 0 3px #000000;
}
#cssmenu > ul > li ul a {
  color: #333;
}
#cssmenu .has-sub {
  z-index: 1;
}
#cssmenu .has-sub:hover > ul {
  display: block;
}
#cssmenu .has-sub ul {
  display: none;
  position: absolute;
  width: 200px;
  top: 100%;
  left: 0;
}
#cssmenu .has-sub ul li {
  *margin-bottom: -1px;
}
#cssmenu .has-sub ul li a {
  background: #f1f1f1;
  border-bottom: 1px dotted #f7f7f7;
  filter: none;
  font-size: 11px;
  display: block;
  line-height: 120%;
  padding: 10px;
}
#cssmenu .has-sub ul li:hover a {
  background: #d8d8d8;
}
#cssmenu .has-sub .has-sub:hover > ul {
  display: block;
}
#cssmenu .has-sub .has-sub ul {
  display: none;
  position: absolute;
  left: 100%;
  top: 0;
}
#cssmenu .has-sub .has-sub ul li a {
  background: #d8d8d8;
  border-bottom: 1px dotted #e7e7e7;
}
#cssmenu .has-sub .has-sub ul li a:hover {
  background: #bebebe;
}

这是html

<div id='cssmenu'>
  <ul>
  <li class='active'><a href='index.php'><span>Home</span></a></li>
  <li class='has-sub'><a href='services.php'><span>Services</span></a>
  <ul>
  <li><a href='employee-benefits.php'><span>Employee Benefits</span></a></li>
  <li><a href='associate-benefits.php'><span>Associate Benefits</span></a></li>
  <li class='last'><a href='safety-training.php'><span>Safety Training</span></a></li>
  </ul>
  </li>
  <li class='has-sub'><a href='about.php'><span>About</span></a>
  <ul>
  <li><a href='who-we-are-and-what-we-do.php'><span>Who We Are and What We Do</span></a></li>
  <li><a href='presidents-statement.php'><span>Presidents Statement</span></a></li>
  <li class='last'><a href='vice-presidents-statement.php'><span>Vice Presidents Statement</span></a></li>
  </ul>
  </li>
  <li><a href='career-opportunities.php'><span>Career Opportunities</span></a></li>
  <li><a href='projects.php'><span>Projects</span></a></li>
  <li><a href='links.php'><span>Links</span></a></li>
  <li></li>
  <li class='last'><a href='contact.php'><span>Contact</span></a></li>
  </ul>
  </div>