Why was there tension between Catholics and Protestants in Elizabethan times?

Here comes a little bit of my History knowledge, helped a little by Google, coming your way!

So, why was there tension between Catholics and Protestants in Elizabethan times? 

Well, Queen Elizabeth I was a Protestant, her elder sister Queen Mary had been a catholic. Before Elizabeth came to power, her sister had been trying to convert the country of England back to Catholicism, which had been the country's main religion before the Henrican Reformation, caused by, you guessed it Henry VIII. 

Anyway, there was tension between the two forms of religion because the Catholics followed the Pope whereas the Protestants rejected him as their spiritual leader. Additionally, Catholics felt that the church and his people, e.g. the Pope etc, could grant them salvation whereas the Protestants believed the only way of achieving salvation was through a direct relationship between themselves and God. 

Basically, Protestants and Catholics are the same form of religion, Christianity, but, they believe in different ways of showing their support and devotion to God and felt the way of the other religion was wrong and therefore shouldn't be followed.