Trenitalia operates a train from Fabro to Florence every 4 hours. Tickets cost $12 - $26 and the journey takes 2 h 9 min. Alternatively, you can take a bus from Fabro to Florence via Fabro-Ficulle, Chiusi-Chianciano Terme, and Siena in around 5 h 6 min.
From Fabro bus to Fabro-Ficulle then train to Firenze S.Maria Novella. 3 h 18 min 19€. From Fabro bus to Fabro-Ficulle, train to Chiusi-Chianciano Terme, bus to Siena, then bus to Firenze. 5 h 6 min. From Fabro drive to Florence. 1 h 21 min 21€.