I solved the problem strictly with CSS and now it works on Firefox and MS Explorer. So far I still have to do two reviews before I can get my site reviewed, but hopefully in the next few days

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But here is the code for the navigation. It is not a dropdown menu, but static with one sublevel. I use this stylesheet as a template for Typo3 CMS.
#navigation {
padding: 0px;
float: left;
margin-top: 2px;
margin-left: 30px;
}
#navigation ul {
margin: 10px 15px 10px -30px;
padding: 0;
background-color: transparent;
}
#navigation a {
border: 1px solid #990099;
margin: 2px 5px 12px;
font-family: sans-serif;
font-style: normal;
font-variant: normal;
font-weight: bold;
font-size: 1em;
line-height: normal;
font-size-adjust: none;
font-stretch: normal;
color: #000000;
text-decoration: none;
display: block;
background-color: transparent;
}
#navigation ul li {
list-style-type: none;
list-style-image: none;
list-style-position: outside;
width: 153px;
z-index: 100;
float: left;
position: relative;
background-color: #bbc7ff;
}
#navigation ul li a {
border: 1px solid black;
margin: 2px;
padding: 0;
display: block;
background-color: transparent;
}
#navigation ul li a:link, #navigation ul li a:visited {
border-color: #ff8040 #668cb2 #668cb2 #ff8040;
border-width: 1px;
margin: 0;
padding: 3px;
background-image: url(linkbg.jpg);
color: black;
text-decoration: none;
width: 100px ! important;
height: 15px;
background-color: #ffffff;
}
#navigation ul li a:hover {
text-decoration: none;
color: #ffffff;
background-color: #000037;
}
#navigation ul ul {
background-color: #33cc00;
display: inline;
float: none;
position: relative;
}
#navigation ul ul li {
margin-left: 10px;
display: block;
background-color: transparent;
width: 100px;
margin-right: 10px;
margin-top: 0px;
float: left;
position: static;
}
#navigation ul ul li a:link {
opacity: 1;
width: 90px ! important;
background-color: #ffffff;
display: block;
background-image: none;
}
#navigation ul ul li a:visited {
opacity: 1;
width: 90px ! important;
display: block;
background-image: none;
background-color: #ffffff;
color: #ff9900;
}
#navigation ul ul li a:hover {
text-decoration: none;
color: #ffffff;
background-color: #000037;
}
#navigation ul ul li a {
font-weight: normal;
}