Is 'Muslim' a proper noun?

In English the name for an adherent of a religion or sect is capitalised thus Buddhist, Christian, Jew, Muslim, Catholic, Protestant.

Thanks, contrex.

What is the difference in meaning between a religion and a sect?

Thanks.

A sect is a group of people with somewhat different religious beliefs (typically regarded as heretical) from those of a larger group to which they belong. Strictly speaking, Catholicism is a denomination rather than a sect.

Thanks, contrex.