The Fire Bottle is a thrown incendiary that carries over the Red Dead style firebomb into a modern setting. It shatters on impact and spreads flame across the ground, so it works for area denial or flushing enemies out of cover. As a thrown item it is simple, cheap, and best used when you want to cover space rather than hit one target.
Thrown weapons like this are typically found in the world or bought in small quantities once available. Rockstar has not detailed GTA 6 store stock yet, so expect to pick these up rather than build a large stockpile early.
The community companion for Grand Theft Auto VI. Database, maps, guides and tools for Vice City and the state of Leonida.