Usually those artifacts are holes; in the illustration below i rendered a sphere with the polygon boundaries made visible and "smooth polygons" set to on in the render settings. The holes occurr when the mesh tears at the boundary of polygons and are visible as white dots (where the thing behind them shows through). Although those are bugs (errors) in Firefly (poser's render engine), and fireflies also are bugs in other render engines, those are not fireflies in the common sense (every firefly is a bug, but not every bug is a firefly).