Google AdSense not working with Firefox 2

I have a little bit modified version of this theme working on http://www.polibuenopolimalo.com/node, but I have tried with this original version and the problem stills remain.
The problem is Google adsense ads displays pretty well with IE7 but doesn't work with Firefox 2. In Firefox 2 I only can see the ad place holder when you are logged in as the admin and nothing as anonymous user. What's wrong??
You can see the problem at http://www.polibuenopolimalo.com/node