I had an issue with my design website: FancyBox was broken on FireFox and Internet Explorer. It worked fine on Chrome, my daily browser. It turned out there was a conflict with the venerable Download Counter plugin for real-time web analytics package Mint running on the main domain. Download Counter rewrites the anchor HREF to redirect through a PHP script, which breaks Fancybox’s (and prettyPhoto’s) attempts to load the image. Quickie solution: configure Download Counter to ignore image files. Then cuss a lot until you feel better :-) I used Firefox’s “inspect element” command, which revealed the otherwise-invisible HREF voodoo.
Photo Gallery Plugins and Mint