The Italy international shot-stopper has left the Sicilians on a temporary basis, and will be accompanied by midfielder Francesco Della Rocca at the Stadio Artemio Franchi
Head coach Vincenzo Montella was keen to add another goalkeeper to his squad ahead of the new campaign, and the former Roma striker has now got the reinforcements he was looking for.
Viviano joined Palermo from Inter on a co-ownership deal in January 2012, and immediately became first-choice shot-stopper with the Sicilians.
Nevertheless, the 26-year-old will now continue his career at Fiorentina after completing his temporary move.
The Viola have also signed midfielder Francesco Della Rocca from the Eagles on a one-year loan deal.
The 24-year-old, who is co-owned by Bologna, was no longer needed at the Rosaneri, and will be looking to relaunch his career at the Stadio Artemio Franchi side.