Okay, figured it out

Okay, figured it out. Stylesheets usually have the .css extension but when you're working on Yahoo! GeoCities that's a lot of hassle - you have to upload a new file every time you want to change the stylesheet. So I called mine style.html so I could use the GeoCities built-in HTML editor to change it more conveniently. Now, Yahoo! is stupid, and adds (broken) HTML and JavaScript to the top and bottom of any HTML page that you load. This stuff can't be removed, so it results in a non-CSS-compliant stylesheet which Mozilla can't handle. My solution? I'm moving the site elsewhere.