Charts in Post Affiliate Pro are displayed using Flash.
There could be more reasons, why flash is not played in Firefox, but works fine in IE:
1. You don't have flash player installed for Firefox - to fix this just install latest release of flash player from Adobe web site
2. You have installed Firefox plugin called Addblock. It is known issue, that Addblock plugin doesn't allow to play some flash objects even the site is whitelisted. Solution in this case is to remove Addblock plugin from firefox and restart Firefox. After restart should be displayed all charts correctly.