@Blaze@caos The federation between Firefish and Lemmy is problematic. According to a #Firefish admin, this is because Firefish requires "Authorised Fetch", which #Lemmy has not implemented correctly. Here from Friendica it works fine.
Lemmy does not implement AF but AF is not a requirement on Firefish (admins can choose to enable or disable it, unlike say GoToSocial which forces it on)
That said, this is still a massive flaw in Lemmy and not having AF enabled on the non-Lemmy side makes defederation essentially useless (which is bad considering the kinds of places that have already set up shop on those parts of fedi), so I personally don't think the trade off of "federating with Lemmy" is worth it.