If you consider Napoli's points in the past five games, you will know that Fiorentina have been a better side. Napoli have gotten just four points while the other team have acquired six points. Except Napoli improves in his game, I doubt if they can become champions this season.
That is only based on the last five games but this is a championship that involves many games so whatever they do in the last five games does not help much. I believe it will be much harder for Napoli to chase the Scudetto because Inter Milan will definitely not make the chances they have achieved and both will definitely work hard for better results to close the competition this season.
Facing Fiorentina is a must for Napoli to get a win even though the game will be much more difficult. But if you look at their current abilities I am sure Napoli will win the game because they will fight harder to get the three points.