I have a self-hosted installation on my Wordpress site. When trying to run the zenphoto setup at this url:

http://the12stepbuddhist.com/zenphoto/zp-core/setup.php

I get this error:

Redirect Loop

Firefox has detected that the server is redirecting the request for this address in a way that will never complete.

The browser has stopped trying to retrieve the requested item. The site is redirecting the request in a way that will never complete.

* Have you disabled or blocked cookies required by this site?
* NOTE: If accepting the site's cookies does not resolve the problem, it is likely a server configuration issue and not your computer.

Not quite the same, but I get an identical page when I log in to this support forum with Firefox. The login seems to go through fine though so when I press the back button and refresh, I'm then logged in.