Same problem here (Firefox 16.0.1) except that I just now noticed that I'm not seeing any ads whatsoever, not just the top banner. That's cool and all, I suppose, but whatever's going on is making all pages load really slowly for me.
Also, for what its worth, I'm using a Windows XP desktop (at work).
For comparison purposes, I launched the site using IE 8 and, while I still don't see any ads, it loaded much faster (damn it!).
To rule out the possibility that it was my company's network settings that were blocking the ads, I launched the site from my iPhone on cellular (turned Wi-Fi off) and I could see the ads on the mobile site but they disappear when I switch to the full site.
Oh, and I don't have Chrome or Safari on this machine so I can't test either of those.