You can still use the Firefly renderer in Poser 12. It's on a different tab in Render Settings.

Some textures look greenish or muddy in newer versions of Poser. There's a script called EZskin that a lot of us used to fix that. It's still being adapted to Poser 12, though. You can instead the diffuse color to white manually. (Usually if you go into the Material Room and check, there's a greenish color in Diffuse Color.)

You should still be able to use diffuse colors and textures in Superfly. The node may be collapsed, but if you click on it and expand it, it's similar to Firefly.