To me, the main difference is that I can’t get Firefish to work.

Firefish has some cool features, but every time I opened it on my laptop the fans would immediately spin up to 100%. It’s not exactly lightweight on the client side.

I don’t use microblogging much but:

• Custom emoji

• Stickers

• Games

• Custom themes

• Cat mode…

edit:
There is table of compare all fediverse software https://joinfirefish.org/

Firefish is much more customisable, both for users and from an Admin point of view. For example, I like that as an Admin I can upload a bunch of emojis that have particular meaning to the instance theme. I can also create a site wide theme (but users can change that if they want to). I can follow people and interact with people on any microblogging service that runs activitypub (so Mastodon etc). I found installing Firefish very easy, using their ubuntu installer .sh file.

There’s absolutely nothing wrong with Mastodon, its great software. I just find firefish more versatile.

@Meowmoth I would say feature bloat. If you need social network message service and want fast loads and less mobile traffic/device resources usage then Mastodon is a king with very tried and true nature. Firefish is fork of Misskey so I can tell a bit as Misskey user. If you want everything in one social service then Misskey/Firefish is the one. Build-in rss reader, memos, gallery, pages, channel for chat like experience, plugins, minigames, likes=emoji that convey message, so… Feature bloat.

Commented here to learn more.