Editing Portable FF

I have been having trouble modifying my portable firefox, I dont know if this is "allowed" by the creators, but I cant even use the INIs. Well, I can edit them but as soon as I restart Firefox, they revert to the old version.
My Main problem is that I am trying to edit the loading screen that is the picture of Portable FF and the USB cable, I edited and overwrote the file but when i Loaf Firefox, the old picture always appears. is there an imbedded file that I need to change? Please help me.