On some Middle Eastern airlines they have a special 'prayer area' in the plane. I've flown on Kuwait airways 777 and they have a small area for prayers located on the left side of the plane next to door 3L. Don't know what other arab carriers have in terms of this
I haven't seen Mulsim passengers praying on any flight that I've been on, or even in the terminal (U.S.). I've seen plenty Jewish men (forgive my lack of knowledge) [they wear the black hats and often have a beard] praying at the airport (one time up to 10 guys were leaning towards the wall) and planes.