In Chapter 3 of Batman: Arkham Knight, you will have to investigate the Arkham Knight’s crashed vehicle. After doing so, Alfred will inform Batman of a fire that has broken out at the Bristol fire station on Miagani Island.
This will initiate the Gotham on Fire Most Wanted Mission, which will have you traveling all across Gotham to put out fires lit by a familiar foe.
Miagani Island, Bristol Fire Station near The Botanical Gardens
Head over there in your Batmobile. The fire is located near the Botanical Gardens, and find the electric panel on the south side. Attach the Power Winch, and rev the engine to power the suppression system. This will activate the sprinklers and extinguish the fire.
However, right at this time Firefly will appear, and it seems he’s the mischievous one behind these fires. You’ll now need to chase him down as he flies around. Avoid the areas of the road he ignites as they will damage the Batmobile, and chase him down.
You will need to perform a takedown by getting close enough and ejecting yourself. However, you should only do this when his fuel bar on the right side is depleted to make it easier for yourself.
Perform a Beat Down on the villain once he has been pinned to get 2 WayneTech Points, which will have him eventually running off. There are two more fires to take down. The second one is in Bleake Island.
Bleake Island, Cauldron Fire Station North of GCPD
Alright, now it’s time to repeat the same process again, using the Power Winch to start up the sprinkler system. Once again Firefly will appear, and you’ll have to chase him down for a second time.
Repeat the same process of taking him down when you’re close enough, beating him up to collect 2 more WayneTech points. The stubborn little bugger will fly away once again, and there’s a third fire to put out in Founders’ Island.
Founders’ Island, Otisburg Fire Station South of Wayne International Plaza
Once Founders’ Island is accessible via the Batmobile, drive there to the Otisburg Fire Station.
Use the same process as before to run the sprinklers, and once again chase after Firefly. This time around, Batman will end up delivering the foe to the GCPD, which will also get you the final 2 upgrade points and end the mission.