The cause of this behavior is the fact that Poser objects are very, very small. Try importing a Poser .OBJ directly into another 3D app - it'll be extremely small. For example, when I import into 3DS Max, I scale up by a factor of 250, so a human figure will be about 6 feet tall in the Max universe.
Firefly is not a render engine developed by Curious Labs, its origins are 3rd party (used to be called Vortex, as far as I remember). So it's not surprising it was not built from the ground up to render these extremely small objects.
I'd say it is a fundamental flaw in Poser, not a Firefly bug.

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