The standard XSP.css that is installed on the Domino server in 8.5 and 8.5.1 contains an error that is highlighted when you use Firefox. The HEX code for the color Black is incorrect: it only has 5 zeros instead of 6.
color:#00000;#
/*** XSP SECTION.<?> ***/
.xspSection{}
.xspSection-header{cursor:pointer;}
.xspSection-header-underline{}
.xspSection-header a{text-decoration:none;color:#00000;font-weight:bold;}
.xspSection-header a:hover{text-decoration:underline;}
.xspSection-wide-header{border-bottom-style:solid;border-width:1px;border-color:#e0e0e0;cursor:pointer;}
.xspSection-wide-header a{text-decoration:none;color:#00000;font-weight:bold;display:block;width:100%;}
.xspSection-box-header{border-style:solid;border-width:1px;border-color:#e0e0e0;cursor:pointer;}
.xspSection-box-header a{text-decoration:none;color:#00000;font-weight:bold;display:block;width:100%;}
.xspSection-tab-header{margin:0px;border-bottom-style:solid;border-width:1px;border-color:#e0e0e0;cursor:pointer;}
.xspSection-tab-header a{text-decoration:none;color:#00000;font-weight:bold;}
.xspSection-tab-header-layout{border:1px solid #e0e0e0;padding-bottom:2px;padding-top:5px;background-color:#f0f0f0;-moz-border-radius:4px 4px 0px 0px;}
.xspSection-tab-header-layout-underline{font-size:5px;height:0px;background-color:#f0f0f0;}