About metagame effect the firearms could cause the end of melee fighters, and players creating their own homebred magic tricks to help spellcasters against gunslingers.
About lore nations could start genocide against evil races as gnolls. (and I wouldn't blame it when these are too evil beyond redemtion or reinsertion). Some races to survive would accept lycantropy curses to be bulletproof, for example werehyenas gnolls, gobling wererats, orc wereboards or drow werespiders. Or infernal cults could be gun-runners selling firearms to evil tribes to cause troubles in a neighbour country.
Other matter some factions wouldn't like the firearms because these are a menace against their own power: undead lords, faes, dragons, giants. Even the own gods could order some limits to avoid pollution...or climate change.
Have you thought about games where PCs are "jungle heroes", tribemen or living in Hirborian civilitation and they have to face invaders with unkwnown technology? Let's imagine the D&D version of "War of the Worlds".
Usually magic is more expensive than technology.
What if anybody want in their setting alchemy to create modern materials as graphene or artificial spidersilk?