<link> not working in firefox?
I don't know that this will fix your problem or not, but a couple pointers I've found while working with external style sheets:
1. keep your words lowercase within your quotes:
<link type="text/css" rel="stylesheet" href="stylesheet.css" />
2. try to list your attributes in your <link> logically, call the type, then rel, then link to it.
3. try to list your <link> and <script> tags last in your header (yes, even after your <title>), just to be sure there is nothing interfering.
hope this helps!