The Catholics, of course, were not protesting anything, they liked things the way they were. Catholic people, as the word implies, were more inclined to be liberal, open-minded, and accepting of other beliefs. If you look up the word catholic, aside from the reference to the church, you will see this definition.
Protestants were far from being liberal and broad-minded. If you were going to be a protestant, you had to show it. The first thing that they did was to insist on being plain. Rituals and graven images were forbidden. Of course, in the years since then, Protestants have lightened up a bit. But a Protestant church was not to be luxurious. There was to be no images of God, or Jesus. Just a Bible on a plain table. There were to be no Popes or Priests. Even the speech was to be plain. The 1611 translation of the Bible by King James, although it may seem like decorative language to us today, was pretty plain.
Of course, people being what they are, this all evolved into a lot of confusion, and ultimately hatred, between the two groups. But Protestants and Catholics both worship the same God, and believe in Jesus Christ as savior. And that means that the similarities so vastly outweigh the differences that they are hardly noticeable.