Sorry to bump this post -
I have kept a European species of firefly in the past (Lampyris nervosa). Larvae fed exclusively on small snails (easy to get in open fields and meadows). Adults did not accept any food. The nice thing was that the females were parthenogenetic so even with no mating they still laid eggs that would later hatch into larvae.
The only tip I can give to anyone trying to breed fireflies is to keep the larvae's container clean. They seems to secrete a chemical when hunting to avoid the snail mucus. If you leave the remains after their meal (shell and what's left of the snail) in the container it really starts to stink after a few days, and the fumes apparently kill the larvae.
Btw, all stages of many firefly species can produce light, even the eggs and pupa.
