You can also go to the Mall by train. You need to get a ticket to Rignano sull'Arno from Firenze SMN station. Trains go every 30 minutes and you need the Arezzo train, the price is about 8 euros return. When you arrive at Rignano there should be a taxi/minibus waiting to take you the 5 minute drive to the Mall for 10 Euros. There is also a local bus service and there are taxis at the Mall to take you back to the train station. I had not realised before i went to Florence that the Prada/Miu Miu outlet at Montevarchi is on the same train line abt 20-30 minutes further down the track, making it possible to cover the two destinations on the same journey. If you just want to go to Prada though your best bet is to catch the Milan train and get off at Montevarchi - its a quicker journey.