Hello this sounds like Pyracantha scab which affects the leaves as a rule but later in the year will affect the berries, have come across this numerous times over the years whilst on my rounds, and i would say from my observations that some years are good some are bad, you can spray with a fungicde if you so wish, try and clear all fallen leaves which are affected and put them in the recycling bin not the compost bin, if you want to reduce the height/width of the pyracantha then you can cut right back, the width could be cut back from six feet to one feet , looks harsh but responds very well, the height too can be greatly reduced if desired, this is known as renovation pruning, i would carry this out next spring, after two weeks new shoots will appear and by the end of the summer it will be all foliaged up, clip the long new shoots mid season to encourage a nice compact frame, once achieved then following years and correct pruning will reward you with plenty of flowers/berries.

Lol....I think myself and Julien are agreed. This is a hardy plant you can cut it right back, in fact it should be cut back every three years or so.