From http://forums.whirlpool.net.au/forum-replies.cfm?t=681721 I saw the below problem:
<table border="6" width="100%" id="table1" height="324" bordercolor="#000000" cellpadding="0" cellspacing="0" style="border-collapse: collapse" bordercolorlight="#000000" bordercolordark="#000000">
<tr>
<td bordercolorlight="#000000" bordercolordark="#000000"> </td>
</tr>
</table>
"Basically firefox seems to always put a light/dark colour on the table border no matter what I do."
Way 01: use cellspacing + td>bgcolor
Way 02: use cellpadding + td>bgcolor