FireFish is a microblogging system similar to Mastodon and Twitter. It's based on the MissKey software that is very popular in Japan. You can think of it as Mastodon turned up to 11; there are so many ways that it improves on Mastodon, making it look better and be more fun to use. Because of this, you might take a look at what I've already written for Mastodon. If you're not used to how the Fediverse works, you can look at that. Firefish used to be called Calckey. The main instance is at firefish.social.

Here are some of the ways it improves on Mastodon:

• It uses MarkDown so you can have rich text with MFM (Misskey Flavored Markdown). Beyond just rich text, it allows you to change the font, have sparklies, and have text spin.
• Channels are like discussion rooms setup on the server (instance). They're local to that server (they don't federate). They're kind of like subreddits.
• Antennae are custom feeds that you create. They're like lists from Mastodon, but you can also follow hashtags. This one is a gamechanger.
• Chat with other CalcKey users.

Here's a guide I found.