@Lando iceshrimp is a fork of firefish with a lot of performance fixes and some things refactored on the back end that will allow it to scale. It also fixes some bugs with firefish, like translation, some aspects of the mastodon api compatibility (makes mastodon mobile apps work more seamlessly), and perhaps most importantly, it has a vibrant development community rallying around it. Firefish, while not dead, has not been moving fast on fixing known issues or implementing new features.