Looking for direct flights to Firenze from the U.S.

You will have to make a connection. This airport does not handle the large jets, all flights are from Europe or London.

..from Europe and London
I know about Brexit, but I don't think London is moving to the Americas.

Regarding the OP's question:
Only Rome (FCO), Milan Malpensa (MXP), Venice (VCE) have intercontinental flights from North America, so for Florence (FLR) you need to connect via a European hub.

Actually, London, which will remain geographically in Europe even after Brexit, is not a good one, because neither Heathrow nor Gatwick, the two London intercontinental airports, have currently flights to FLR.

Better hubs would be:
CDG, FRA, MUC, AMS, ZRH, all of which have at least 4 flights a day to FLR.

Of the 3 Italian intercontinental Italian airports mentioned above, Rome (FCO) is the closest to Florence and the fastest to reach Florence by train (about 2.5 hours from the FCO airport station with one change at Roma Tiburtina station).

Try Pisa or Venice, or Milan, or Rome.

Pisa no longer has the direct link. Delta discontinued the daily seasonal flight from Pisa to JFK last year.

There are no direct flights to Florence from the USA. You have to make a connection. I have found that flights from USA to Milan are the most affordable, and then a short hop from Milan to Florence

The short hop from Milan to Florence mentioned by Jim will be either on a train (about 3 hours from MXP with a change at Milano Centrale), or on a car if you plan to rent a car (4 hours).

There are no flights from MXP to FLR.

Hello! Where are you flying out of? I just purchased flights from DFW to Rome- albeit not a direct flight, but, better than connecting in NYC. Train ride is quick and very reasonably priced. Good luck!