Firefly was a fire-starting criminal. He appeared in the DC Animated Universe several times, and was voiced by Mark Rolston.
Garfield Lynns was a special effects and pyrotechnic expert who worked on the road with the pop music artist, Cassidy. Lynns nursed a love for Cassidy. Her flirtatious behavior only fueled Lynn's obsession. After a date or so, Cassidy and Lynn's relationship became strained. Cassidy then finally decided to lay off Lynns after she opened for Gotham's Rock City Nightclub. Lynns overrode the pyrotechnic displays and fled the scene. In secret, Lynns worked on an insulated battle suit that was capable of flight and took the name, Firefly.
Lynns used his cache of flash caps, napalm accelerators, and smoke bombs, as well as a rig that generated a blade-like flame. Intent on fleeing Gotham with Cassidy, Firefly decided to use an experimental gel, of his creation. The gel was capable of burning through anything and he planned to flood it into the sewers and burn all of Gotham in one swoop. However, Batman intervened and stopped Firefly. Soon after, Firefly, out of prison, began to contract out as an arsonist for hire in Gotham. After the fire was set, his clients committed insurance fraud and profited heavily. The local newspapers documented them as 'mystery arsons' and caught the attention of three young children who mistook the shadowy figure in the picture as Batman. The children followed Firefly to one of Gotham's theaters and witnessed Batman's arrival. Batman saved the children and stopped Firefly again.
Some years later, due to prison overcrowding issues at Stonegate Penitentiary, Firefly was transferred to Stryker's Prison in Metropolis. A prison riot soon after, allowed several super villains to escape. Firefly was paired with Volcana, with whom he shared a casual interest in. The super villains caught the attention of the Justice League. Batman and Green Lantern arrived to confront the pair as Volcana attacked a Metropolis Special Crimes Unit detachment. Stewart trapped Firefly and Volcana in a ring construct in an effort to render their namesakes useless. However, both fought anyways and exhausted the trapped oxygen. Firefly and the rest of the super villains were recaptured and returned to Stryker's.
Firefly soon ended up joining The False Face Society. His first assignment was to torch the club of Boxy Bennett, after the crime boss had refused to pay Black Mask protection money. Batman infiltrated the False Face Society as Matches Malone, and learned of Firefly's next assignment. Batman then proceeded to Firefly's hideout and sabotaged his equipment. When Firefly tried to torch the club, his weapons refused to work when Batgirl showed up to thwart his plan. Firefly attempted to escape via his jetpack, but Batman struck a match to his exhaust trail, and turned it into a burning fuse due to Batman's earlier sabotage. Firefly crashed to the ground after his jetpack exploded and was captured by Batgirl.
While Firefly did not appear in Batman Beyond, his costume was seen on display in the Batcave during the episode "Black Out". During a battle between Terry McGinnis and the shapeshifting villainess Inque in the Batcave, the glass case that contained Firefly's costume was smashed, and his outfit was supposedly buried in the falling debris.