A word to my fellow travelers going to Florence, the busses and trams have convenient "Tap & Go" stations on all of them.
Two things to know, the ticket at those stations are twice the price of buying a paper (90 minutes) ticket either from a tobacco shop or machine on the tram stop.
Second, the payment is only for ONE TICKET even if you Tap twice. A 40 Euro fine per person for non-ticketed travel. (Yes, I got fined)
Best of Luck!
Ciao