I m not so strong with engligh but having problems with your addon.
i found in your addon only the file "lightbox.pxp".
I uploaded your file and enabled it.
No we have only add your tag <LIGHTBOX_THUMBNAILS> in my file "browse_template" isn't it???
But i think this instructions are not completed, now i read should be also a file lightbox.js ?? where we tale it? and a new css??
Sorry for misundestanding but i wish you explain better how your addon works,