Can't speak to the NES, but the GB/GBC definitely has a boot ROM with firmware that remains operable without a cartridge in the system. (The SGB has a different

Can't speak to the NES, but the GB/GBC definitely has a boot ROM with firmware that remains operable without a cartridge in the system. (The SGB has a different one that shims into the slightly different SGB hardware itself. Also, if you've never read about the SGB, that thing is kind of wacky; it's basically a Game Boy that delegates colorization and, in some games, audio and multiplayer to the Super NES.) The GB/GBC boot ROM doesn't do as much as even, say, the GBA, but if you're talking "conceptual" about firmware, we're talking about a pretty unbroken line to the current day. (Modern game consoles also have operating systems, but those aren't firmware.)