There are several definition of MCT. One is the legal MCT allowed by airlines so that flights can be on the same issued ticket. Another one is the reasonable MCT to give you a good chance to make the connection. As suggested by Bankops, 75min is legal. But it is very tight if the JFK flight is ontime. However, JFK tends to be very busy in the evening and long tkeoff delays are not uncommon. However, if both flightsare on the same AF ticket, AF will protect you and put you on the next FRA flight. There are many of those, so don't worry. With Skypriority, it is faster to clear immigration, but you need to have Skyteam status.