I've posted this at the official efiction forums, too, but I thought it would be worth posting here.
I'm pretty sure it has to do with the CSS, although I don't know how... I mostly just edited the colours from the stylesheet of one of the skins that came with the script :/
BODY {margin: 0; color: #141720; background: url("
http://www.starrydollz.com/hpff/skins/Hogwarts/hpbg.png"); width="750" padding-left: 2em 0em solid transparent; text-align: left;}
#main a {color: #242D42; no-repeat left; padding-left: 0px; padding-right: 0px; text-decoration: none; font-weight: bold; }
#main a:hover {color: #334467; no-repeat left; padding-left: 0px; padding-right: 2px; font-weight:bold;}
LABEL { font-weight: bold; margin-right: 0px; "position: abolsute left:center";}
#banner {
background: (
http://www.starrydollz.com/hpff/skins/All%20three/images/hpbannerbg.png");
height: 200px;
text-align: center;
border-bottom: 0px solid #000;
color: #60638A;
}
#sitetitle { font-size: 26pt; display: block; font-family: 'Arial';}
#siteslogan { font-size: 13pt; font-weight: bold; }
#skin { position: absolute; top: 0px; left: center; width: 726px;}
.tblborder { border: 1px solid #000; }
#menu { border-top: 0px; border-bottom: 0px; background: url("
http://www.starrydollz.com/hpff/skins/All%20three/images/hpbannerbg.gif"); border-left: 0px solid #000; border-right: 0px solid #000; width: 750px; border-bottom: 1px solid #000;}
#menu ul {
margin: 0;
padding: 0;
text-align: center;
font-size: 11pt;
width: 719px;
font: Times New Roman;
}
#menu li { style="position: absolute; left:center" list-style: none; margin: 0px; padding-bottom: 0px 0px; display: inline;}
#menu a {color: #000; no-repeat left; padding-left: 3px; padding-right: 3px; text-decoration: none; font-weight: bold; }
#menu a:hover {color: #3F4F6F; no-repeat left; padding-left: 2px; padding-right: 2px; font-weight:bold; }
#mainpage { margin: 0px; background: #3B4151; padding: 0em; height: 450px; width:746px; border-left: 2px solid #000; border-right: 2px solid #000; }
html>body #mainpage { min-height: 450px; height: auto; }
.cleaner, .output { clear: both; height: 1px; font-size: 1px; border: none; margin: 0; padding; 0; background: #252636; }
#footer { background: #3B4151; color: #141720; text-align: left; text-indent: 10px; border-left: 2px solid #000; border-right: 2px solid #000; width:746px; border-top: 1px solid #000; border-bottom: 1px solid #000}
#footer a { color: #242D42; text-decoration: underline; }
#footer a:hover { color: #334467; text-decoration: underline; }
#info { background: #41495D; color: #000; text-align: left; text-indent: 10px; border-left: 1px solid #000; border-right: 1px solid #000; width:670px; border-top: 1px solid #000; border-bottom: 1px solid #000}
#info a { color: #242D42; text-decoration: underline; }
#info a:hover { color: #334467; text-decoration: underline; }
#credit { background: #3B4151; color: #141720; text-align: left; text-indent: 10px; border-left: 2px solid #000; border-right: 2px solid #000; width:746px; border-top: 0px solid #000; border-bottom: 2px solid #000}
#credit a { color: #242D42; text-decoration: underline; }
#credit a:hover { color: #334467; text-decoration: underline; }
#online { background: #242D42; color: #0B101B; text-align: left; border-left: 2px solid #000; border-right: 2px solid #000; border-bottom: 2px solid #000; border-top: 2px solid #000; width:746px}
#online a { color: #000; text-decoration: underline; }
#online a:hover { color: #3F4F6F; text-decoration: underline; }
/* used for the blocks on the index page */
.block { border: 1px solid #000; background: #212942; margin: 0 5%; padding: 0; margin-bottom: 1em; }
.block .title { background: #212942; color: #000; margin: 0; font-weight: bold; padding: 0; border-bottom: 3px double #000; padding: 5px; text-align: center;}
.block .content { background: #242B3C; margin: 0; padding: 5px;}
.newsbox{ padding: 5px;}
#news { background: #41495D; color: #000; }
#news p { padding: 3px; }
#newsarchive { text-align: center; background: #212942; margin: 0; padding: 0; border-top: 1px solid #000;}
#newsarchive A { color: #000; text-decoration: underline; }
#newsarchive A:hover { color: #3F4F6F; }
#pagetitle { text-align: center; font-size: 14pt; color: #0B101B; }
#pagetitle:after { content: "."; display: block; height: 0; clear: both; visibility: hidden; }
html>body #pagetitle:after { display: none; }
#pagetitle { display: inline; }
/* Hides form IE-Mac \*/
* html #pagetitle { height: 1%; }
#pagetitle {display: block; }
/* End hiding */
.respond, #alphabet, #pagelinks { text-align: center; margin: 1ex;}
.respond:after { content: "."; display: block; height: 0; clear: both; visibility: hidden; }
html>body .respond:after { display: none; }
.respond { display: inline; }
/* Hides form IE-Mac \*/
* html .respond { height: 1%; }
.respond {display: block; }
/* End hiding */
#bio { padding: 5px; }
#profile #sort { text-align: right; padding-right: 5px; }
.jumpmenu { text-align: right; margin: 4px; }
.sectionheader { font-weight: bold; text-align: center; padding: 1ex; }
#titlebox { margin: 1ex 2em; border: 1px solid #000; padding: 5px;}
#tabs {
margin: 1ex 0;
padding: 0;
background: #212942;
width: 100%;
}
html>body #tabs { height: 17px; }
#tabs DIV{
width: 33%;
margin: 0;
padding: 0;
float: left;
color: #000;
font-size: 10pt;
background: url() no-repeat right top;
}
#tabs #centertab {
background: #212942;
width: 100%;
}
#tabs a { color: #000; background: url() no-repeat left top; padding-left: 18px; }
#tabs a:active { color: #4B536B; text-decoration: none; }
#tabs a:hover { color: #3F4F6F; }
#tabs #active { width: 34%; padding-bottom: 1px; color: #4B536B; background: url() no-repeat right top; }
#tabs #active a { color: #4B536B; background: url() no-repeat left top;}
#tabs #active a:active, a:hover { text-decoration: none; }
.classification { font-weight: bold; color: #000; }
.listbox .content { padding: 4px; }
.listbox .title { background: #212942; color: #000; font-weight: bold; padding: 2px;}
.listbox .title .classification { color: #0B101B; }
.listbox .title A:link, .listbox .tail A:link { color: #0E1426; }
.listbox .title A:visited, .listbox .tail A:visited { color: #0E1426; }
.listbox .title A:hover, .listbox .tail A:hover { color: #334467; text-decoration: underline;}
.listbox .title A:active, .listbox .tail A:active { color: #0E1426; }
.listbox { margin: 1em 5%; border: 1px solid #000; }
.listbox .adminoptions { padding: 4px; }
.listbox .tail { padding: 2px; background: ; color: #0E1426; font-weight: normal; }
.listbox .tail .classification { font-weight: bold; color: #162136; }
A:link {color: #242D42; text-decoration: none; font-weight: bold; }
A:visited { color: #242D42; text-decoration: none; font-weight: bold; }
A:hover { color: #334467; text-decoration: none; font-weight: bold; }
A:active { color: #60638A; text-decoration: none; font-weight: bold; }
#listings #sort { text-align: center; }
#categories .respond { height: 20px; text-align: center; width: 95%;}
html>body #categories .respond { width: 100%; }
#listings #sort { display: block; width: 90%; margin: 0 auto;}
/* The following fixes the disappearing text bug in IE. */
/* the clearfix class fixes certain problems with display in IE. if you have disappearing backgrounds and/or text in a div adding this class to the PARENT might help */
#output:after, .clearfix:after { content: "."; display: block; height: 0; clear: both; visibility: hidden; }
html>body #output:after, html>body .clearfix:after { display: none; }
#output, .clearfix { display: inline; }
/* Hides form IE-Mac \*/
* html #output, .clearfix { height: 1%; }
#output, .clearfix {display: block; }
/* End hiding */
So... any ideas why it's so messed up in FF?