You probably have to adjust the transparency falloff for anything with transparecy from .6 to 0

In general, I have been unchecking the "turn off back facing polygons" option. It seems to make things look weird.

Rendering while you are in the material room in the little preview window makes material changes less painful to check.

Almost every piece of clothing or prop I have tried requires tweaking in the material room to render with Firefly.

I have been turning off displacement every time when rendering in Firefly.. no idea why it is on by default.