Those who have been around longer may know this. In hindsight I knew it, but Poser fooled me again with it today, so for all newbies and others short of memory like me:

*Firefly produces no render if there is not at least one (1) figure in the scene!  The figure may not be 'hidden', but need not be actually 'seen' by the camera.

*So, if you want to make a quick 'check' render of the props background only, and you want to 'hide' the figure for speed, you will need to add a figure.