I would think your issue probally has to do with your html code and not the browser.
Running your site through w3c's html validator has revealed 566 errors in your html
http://validator.w3.org/check?uri=ht...org%2Fphoto%2F
Maybe the new firefox browser is not as forgiving as older browsers who knows but this is where I would suggest you start. If you turn off the header's and footers around your photopost and just run Photopost I think you will find it views fine in your mozilla 1.5 browsers which will tell you absolutely the issue is with your html coding