I have to agree that the Firefly engine is not rendering correctly with that node arrangement.  The only recommendation I can offer is to reduce the Diffuse value to about 85%, there is no such thing as 100% diffuse.  Try adding an HSV2 node between the Diffuse map and the Diffuse_Color, it will give you a little more control over brightness and saturation.  Double-check the Gamma correction on the maps; Diffuse texture should be using the Gamma value from the render settings, and the default should be 2.2, and the Bump map should be set to the custom Gamma value of 1.  Otherwise, I would hate to think that the tech team broke the PoserSurface.