Firefly is an airline but fireflies are lightening bugs which used bioluminescence to attract mates or prey. Those two are different except that both can fly.
When I was small I used to catch this bugs. I was fascinated by the chemically-produced light from the lower abdomen which I remember always green in colour.
Now, of course, I don’t play with fireflies any more. On the other hand, I had opportunity to fly with Firefly on several occasions. On the first occasion using Fokker F50 aircraft many many years back and fairly recently using ATR 72-500 aircraft from Sultan Ismail Petra airport to Subang. Compare to 737 aircraft, the seating in ATR 72-500 aircraft is just 2-seater on both side of the cabin. Here, the refreshments are included in the bill. The ritual of informing customers about emergency procedures is similar to Malaysia Airline, the parent company of Firefly.
The reason for choosing Firefly for many people is to save cost on travelling. True enough, for those who book late the price is found to be reasonable compare to another low cost air plane.