I did exactly what you described you did for Firefish. I think it depends if someone on your Firefish instance has subscribed to that Lemmy community before or not. When I opened the @fediverse@lemmy.world profile I saw all the posts and replies listed and just replied to the post from there.
Xepher
0 Post – 3 Comments
Joined 1 years ago
Hmm... I wonder if Mastodon only loads the replies from the original instance the post was created on?
@sebitoutou@programming.dev
I'm replying to this from Firefish. Also reacted with a 🔥 emoji, so we'll see how that works (if at all)