True, displacement didn't exist in P4, yet Firefly seems to smooth every texture it renders, at least on my machine. Including textures that have bump map (not displacement) applied. Example of this... :

Firefly Render (poser 7) :
http://fc03.deviantart.com/fs20/f/2007/229/5/3/meh2_by_BlueDragoness.jpg

P4 Engine Render (poser 7) :
http://fc02.deviantart.com/fs20/f/2007/229/5/a/meh_by_BlueDragoness.jpg

(Look at the yello crest, and the metal up between the pauldrons and breastplate - it's most obvious there.)

Render Settings.......

Firefly :
Use Displacement Maps : Yes
All Else Default on the 'Automatic' settings.

My 'manual' settings for Firely are :
Cast Shadows : Yes
Ray Tracing : Yes
Min Shading Rate : 0.2
Raytrace Bounces : 2 (Default setting)
Irradiance Cacheing : 50 (no clue what this does - haven't changed it - that's default)
Pixel Samples : 3
Max Bucket Size : 64
Use Displacement Maps : Yes

My Poser4 Render Settings (also in Poser7) :
Anti-Alias : Yes
Use Bump Maps : Yes
Cast Shadows : Yes
Use Texture Maps : Yes
Ignore Shader Trees : No