A user from my instance cannot follow an account using microblog.pub. On her end, it gets stuck at "processing". If I take a look at the dashboard, it used to show a failed job, with the error "invalid follow URI".
I'm not sure whether the problem comes from microblog or Firefish, but there is a similar known issue with Chirp and Guppe groups, and Firefish's main developer said that it was a problem on their implementation of ActivityPub.
I tried to follow an account using my profile (the job stopped appearing after a while for her follow request), I can show you the data I receive on Firefish.