36 years ago - Garfield Lynns is born.
25 years ago - 11-year-old Garfield first exhibits accute pyromania.
18 years ago - 18-year-old Garfield enlists in the army, joining the Rangers.
13 years ago - 23-year-old Garfield is discharged from the army for psychological reasons. He begins his career as a pyrotechnician.
12 years ago - 24-year-old Garfield is hired for the road crew of pop singer Cassidy who he starts to date.
.10 years ago - 26-year-old Garfield is burned in a pyrotechnic accident, Cassidy leaves him, and he starts building his equipment to have his revenge.
8 years ago - 28-year-old Garfield attacks his ex-girlfriend Cassidy's stage show as Firefly, starting a pyrotechnic rampage across Gotham before he is caught by Batman.
4 years ago - 32-year-old Garfield is among the inmates of Arkham released by Bane. He returns to his hidden lab and uses a new prototype costume to attack the police before he is stopped by Batman.
3 years ago - 33-year-old Garfield escapes Arkham again during No Man's Land, using the destruction of the earthquage to start fires across the city before he manages to escape.
Firefly is a pretty solid comic book badguy, but within Batman's pantheon of villains he's probably about C-level at best. He has a cool schtick and a good look, but ultimately he's really just not THAT dangerous when compared to some of the other enemies Batman has to fight. Still, he's functional, has a good backstory, and presents at least a decent physical challenge for Batman to overcome; any story about Firefly will invariably end with Batman trailing behind a dude in a jetpack with a grapping line. It might not be original, but it's certainly satisfying.
Firefly's Comic History
Firefly is actually one of those old classic terrible Batman villains from the fifties, right up there with Crazy Quilt and the Condiment King. In his original origin, Garfield Lynn was a standard street thug who was being persued by Batman and Robin. When the crimefighters saw a lingering firefly in the darkness they assumed it was Lynn's cigarette (it's the 50's), and lost him. So naturally, Lynn decided that he's going to be a firefly-themed super villain and puts on a TRUELY terrible costume... the sort of outfit someone might wear on the sidewalk to promote a seafood restaraunt... and starts staging crimes with light or optical illusion themes. It's funny how this sort of nonsense was fun and cheeky when Flash villains were doing it, but when Batman villains do it is just comes across as frustratingly sad.
It was after the first Crisis that Firefly was reimagined as a fire-based rather than light based badguy, which pretty much immediately resolved the weirdness of the character. When Batman the Animated Series used him in the episode "Torch Song" and defined him as a revengeful pyrotechnician it pretty much established the character as we have him today.
Our Firefly Story
We actually didn't invent a single element for Garfield's timeline. We've simply taken the given facts of the character: that he is a lifelong pyromaniac, he was a special forces soldier that was discharged because of his psycological issues, had a career as a pyrotechnician for a pop singer who rejected him... we just laid those out together and they took shape into what his life would have been.
From there, you'll notice that there actually isn't a single story after his introduction where he is the sole badguy. This is actually the best way to go about using the character; After the drama of his initial appearance reaches it's climax he doesn't really bring any of his own narrative weight. What he IS, however, as a great outlier part of the world of Batman that can bring a whole new layer of complication to a larger story. For all of the major Gotham-wide storyarcs where multiple enemies have escaped are are turning the city into a crisis-zone, Firefly is a great element to add. He brings a entirely different dimention to the physical challenges Batman has to confront. There's never any question as to whether the hero will win, but that's really the case all the time, anyway.