Good question! Whether it’s actually infringement is a legal judgment I’m certainly not qualified to make. 🙂 But my understanding is that it hinges on whether a court thinks a “reasonable person” could be confused. For example, a clothing brand called “Firefoxy” would probably be in the clear since Mozilla isn’t in the clothing business. And maybe even a clothing brand named “Firefox” might be okay! For example, Apple Computer and Apple Records (founded by The Beatles) coexisted nicely for a long time until Apple Computer started getting into the music-selling business. I forget how it got resolved (maybe a licensing agreement?) but The Beatles’ music wasn’t available on the iTunes Music Store for a looooong time while that dispute was going on.
Firefish is an online service and software package, the very space Mozilla operates in, so there’s at least a case to be made that reasonable people might incorrectly assume it’s from Mozilla. It’s come up many times in this discussion already, and we as active Fediverse users are already pretty well informed about this!
I don’t know anything about gnomes and barely anything about TTRPGs, but this question makes me think about social vs. medical models of disability. In our modern-day society, the social model would mean that autism is only a “disorder” because society doesn’t accommodate our needs well enough (or, sometimes, at all). It isn’t a disorder to be allistic because it’s “normal”, “the default”, nothing more than that. For example, in a hypothetical society where people widely use language very literally, the behaviour of not taking things literally could be labelled a disorder. Or if the vast majority of people had sound sensitivity, then someone without it who often forgets to keep their voice down might be seen as disordered. So if you do decide to go with this idea, I think there might be something to explore there when gnomes are interacting amongst themselves vs. with other groups.
If you’re concerned about “game author compares autistic people to gnomes”, is there a different class to use that might be a better choice? (I have no idea, but it sounds like maybe gnomes have a negative stereotype?)