Instead of rendering each page under a folder, can be without?

[freereikicourse]

I get all rendered like this mypage.html/index.html. Then some url start looking weird and I get sometimes on the live site with www.xxx.com/mypage.html/ and www.xxx.com/mypage.html. They are the same page but one has a slash at the end the other not.

I wonder if I can make them all without slash at the end.

Thanks