The set clearly states that when using firefly I might experience this problem:

Says:
"""Important note when using the firefly renderer...
 
Due to the nature of the firefly render some of the transparent 2D
props in this package may render with slight black streaks. This is
easily fixed by setting the displacement to 0.01 in Poser 5 for the
object and attaching to the displacement node. Poser 4 users and
Poser 5 users rendering with the Poser 4 renderer will not notice
any streaks."""

So I went to add a displacement node - but which one???  Or what type?  I am using Poser6 btw.

Thanks in advance.

I am:  aka Velocity3d