Often this is a normal interpolation problem. Firefly tends to skip polygons (and together with them their normals) when you have very small faces, like those produced by boolean operations, at least this is my impression. "Small faces" means: in the general size range of your shading rate. Here are some things you can try out:

1 - because your windows have a rim around them: Redo the windows without booleans, or at least make them using less vertices. 16 could be enough, then hide the polygonal hole behind the hi-poly rim. Try to make the faces as big as possible (i.e. when using a boolean-difference, try to keep a distance between the cylinder-window and the rim of the wall-rectangle, etc.)

2 - Poser's edge crease often makes mistakes when calculating the angle between faces, but you can use blender's edge-split modifier (which works a bit better) to split the edges before exporting. You can even use blender to split at every edge (select every edge in edit mode, and then "Mark sharp"). This usually works, but only for flat-faced models, because this effectively disables normal interpolation; you have to try it out to see how it looks. This might generate some problems when using displacement maps by ripping holes into your model. Also your files will become larger.

3 - Simply lower the shading rate in both the object's properties panel and the render settings. This often works, too, but has the Big drawback of slowing down the renderer. Also it depends on the size of the object in the image to determine what shading rate is best. Test if a shading rate of e.g. 0.01 gives the desired effect and if it does find the highest value that is acceptable. If 0.01 is still too bad or just too slow, use another approach.