Representatives of Quantum Mechanix and Spark Plug Games announced this at Comic-Kon. The player will act as the captain of the ship, who should hire new people and perform tasks in the universe inhabited by numerous characters from the series. You can see this in action in a new trailer.
Initially, Firefly Online was announced only for mobile devices based on iOS and Android, but later the authors announced the release on PC and Mac. The release date was repeatedly postponed, and now they plan to release the project in the spring of 2015. The developers explain such delays with the need to recreate several dozen actors in the form of 3D models and a huge amount of voice acting.