Wow, at first blush I don't know what is specifically wrong, and not to sound like an elitist, but you really should start trying to use div's in your css as it would make things much clearer.
My guess however is that it has to do with the way firefox is handling your wrapping of a table within a table. When I extract the table so that it is no longer nested and view it in Firefox
with no css stylings inheirited or otherwise it looks just fine.
HTML Code:
<table class="header-table" cellspacing="0" cellpadding="0">
<tr>
<td>
<!-- what is the purpose of the above table? -->
<table border="0" align="center" cellpadding="0" cellspacing="0">
<tr>
<td><img src="http://www.porncritixxx.com/headers/asianreviews/header_01.jpg" width="736" height="22"></td>
</tr>
<tr>
<td><table width="736" border="0" cellspacing="0" cellpadding="0">
<tr>
<td><a href="#"><img src="http://www.porncritixxx.com/headers/asianreviews/header_02.jpg" width="114" height="90" border="0"></a></td>
<td><a href="#"><img src="http://www.porncritixxx.com/headers/asianreviews/header_03.jpg" width="523" height="90" border="0"></a></td>
<td><img border="0" src="http://www.porncritixxx.com/headers/asianreviews/header_04.jpg" width="99" height="90"></td>
</tr>
</table></td>
</tr>
<tr>
<td><img src="http://www.porncritixxx.com/headers/asianreviews/header_05.jpg" width="736" height="84"></td>
</tr>
<tr>
<td><table width="736" border="0" cellspacing="0" cellpadding="0">
<tr>
<td><img src="http://www.porncritixxx.com/headers/asianreviews/header_06.jpg" width="425" height="23"></td>
<td><a href="#"><img src="http://www.porncritixxx.com/headers/asianreviews/header_07.gif" width="212" height="23" border="0"></a></td>
<td><img src="http://www.porncritixxx.com/headers/asianreviews/header_08.jpg" width="99" height="23"></td>
</tr>
</table></td>
</tr>
<tr>
<td><img src="http://www.porncritixxx.com/headers/asianreviews/header_09.jpg" width="736" height="59"></td>
</tr>
<tr>
<td><img src="http://www.porncritixxx.com/headers/asianreviews/header_10.jpg" width="736" height="72"></td>
</tr>
</table>
<!-- remove the following lines -->
</td>
</tr>
</table>