What happened?!

[Reefhawk1]

You might want to test the LFS water parameters before you add your fish to your tank. Also the shock of the change in temperature from the bag water to your tank could also kill the fish. Another possibility is that it was severly stressed before you bought it, if it was only in the LFS system for a couple of days without quarantine the shock of comming out of a bag after a long shipping period then being introduced to their system at the LFS with unknown acclimation period and then to your tank a couple of days later sent this little guy into a stressful situation.

Sorry to hear for your loss and I hope you find another firefish that thrives in your aquarium.