"vertical-align: middle" does not align to the middle in Firefox
Firefox is rendering correctly. The vertical-align property is inline, which means it doesn't apply to block elements like <div> (and <p>, etc). Try adding display: inline and see if that works.
Vertical align only works as expected on table cells or display: inline-block
elements. If you want more information I suggest you read Understanding vertical-align, or "How (Not) To Vertically Center Content".
Edit: You've got something else going on because that works for me as is on Firefox. I even dropped the font size of SECTION: right down and it's still centered. Have you used Firebug to see what other CSS is affecting it?
This works as is:
<html>
<head>
<style type="text/css">
div.categoryLinks {
margin: 1em 16px;
padding: 0 4px;
border-width: 1px 0;
border-style: solid;
border-color: #ece754;
background: #f7f5b7;
color: #a49f1c;
text-align: center;
font-size: 1.4em;
}
div.categoryLinks em {
font-size: 0.4em;
font-style: normal;
vertical-align: middle;
}
</style>
</head>
<body>
<div class="categoryLinks">
<em>SECTION:</em>
Page One ·
Page Two ·
<a href="link">Page Three</a>
</div>
</body>
Note: section font size changed to 0.4em from original 0.6em to emphasize the point.