FXXX is a New New York satellite TV channel.
In 3014, the Madison Cube Garden with all the Bart-like creatures in it crashed into an FXXX satellite. It's possible that the TV channel has adult programming, which is normally marked with "XXX".
Behind the laughter:
FXXX is a parody of cable channels FX and FXX. FXX broadcasted the Every Simpsons Ever marathon from August to September 2014 and The Simpsons 600 marathon from November to December 2016.