It should work on all firmwares. Honestly every time someone's had trouble getting the emulator to find their firmware it was a naming issue. Alternatively, it also checks for the files in the directory that the .nro is in, so if your .nro is just in the switch directory and not in the melonds directory, you can try putting them there. Other than that, I don't know.
Eureka, that was it, thank you! I'm so used to NROs being placed in the switch folder without additional files {if necessary} having to be in the same section.
Now, I just have to remember not to bump the L button as it keeps freezing my Switch and/or giving me an error code so I have to reboot. Didn't think to write down the code, but I'll do it if I see it again.