I uninstalled old firefox and installed mozilla fitefox 18.0.1(x86 en-us) and I can't open upubs,,,,is there something else I need to do?

I all of the sudden had a problem openning up upub from a trusted website like usual and it would not let me as it did a few days ago using firefox html document default,,so I uninstall old vertion and installed mozillz firefox 18.0.1. This didn't help. Can you brainstorm why I cannot open epub anymore on my desktop windows xp?