Thanks for posting this. It's hard not to become the "but muh firefish" guy every time a thread like this pops up.
Solves nearly every complaint I've seen about the Mastodon interface, has features I haven't even seen folks ask for (I like the "antennas" feature a lot), federated with Mastodon, and will guide you through importing everyone you follow or who follows you - literally migrating your Mastodon account over in just a couple clicks.
I'm not anti-Mastodon whatsoever, but for the folks who find it klunky, Firefish is the answer for sure.