Not a joke, and I didn't know GBARunner3 was a thing already, that's dope! I only recently tried GBARunner2, and it leaves much to be desired since it's a dead project. And I'm talking about the open-source BIOS for the GBA, not the 3DS thing. Sorry If I got the name wrong.
In case it's not a joke, GBARunner3 is being developed from the ground-up, and it should fix most of the issues.
As for open_agb_firm, it's exclusive to the 3DS, it's not possible to get it working on DS, as on DS the cartridge pins are routed directly to the Slot2 connector, while on 3DS it's routed to a cartridge emulator.