It has the better feature set and UX. Some things I like:

• Threaded comment replies (though they display differently from Lemmy’s).
• Antennae for discoverability.
  • Can use hashtags AND keywords.
  • Can filter results by instance.
  • Can create multiple timelines to display content in.
• Customizable UI via widgets.
• I think the theming options are better.
• Full-text search.
• Quote posts.
• Cat mode.

you don’t really have to, but it’s a lot more feature rich, less heavy to run if you’re self hosting, and has a really slick ui to boot

ok but how about you tell me why to move from mastodon to firefish?

I like the UI better (by a lot), I like the “antennas” feature, I like that I can do a traditional blog post if I choose (“pages” they call it), it’s very custom-configurable, and in the 3 days since I’ve joined I’ve already seen bugfixes and improvements deployed.

Why move? If Mastodon is 100% great for you and nothing about the look/feel/functionality of Firefish jumps out at you then there is really no reason.