Are you entering the direct name of the particles, or just "Firefly"? Because "Firefly" by itself is not a particle, the file "firefly.particle" is actually MANY particles.
According the the firefly.particle, these are the particle names:
Fireflywest
Fireflyeast
Fireflynorth
Fireflysouth
Fireflyup
Fireflyupeast
Fireflyupwest
Fireflyupnorth
Fireflyupsouth
Fireflydown
Fireflydowneast
Fireflydownwest
Fireflydownnorth
Fireflydownsouth
Try entering any of the above into the Particle tab of Object Maker. ;3