I am in total agreement with what Hank has said about Florence. Not only is the main tourist area compact, it is, for the most part, pedestrian only. Therefore a bus would be of not uses.
Take a city bus to Academia (1 Euro) and there are several that go there that depart along the street between the train station and the Duomo (via dei Panzani, via dei Cerretani or via Martelli) You want the bus that goes to Piazza San Marco. Not in a big hurry? Enjoy the lovely walk.
Radiance of the Seas - Nov 2006
Legend of the Seas - Jun 2007
Costa Fortuna - Mar 2008
Legend of the Seas - Oct 2008
Celebrity Constellation - July 2009
MSC Orchestra - Jan 2009
Navigator of the Seas - March 2009
MSC Poesia - November 2009
Jewel of the Seas - June 2010