Single player won't respond.

When i go on single player the page keeps not responding. I just bought Minecraft and downloaded it. When I go on it works for a minute then says its not responding. When I re-open the page it works less and less.

What I expected to happen was...:
I expected to go on the game and procrastinate my homework for hours.

What actually happened was...:
I went on for 5 minutes and then it stopped responding. When I closed and re-opened the game it only worked for 2 minutes, then stopped responding.

Steps to Reproduce:
1. Open the game
2. Play the game
3. Wait