The mining page says that but if you actually place the javascript code on your own web page, you will mine in the background when you visit that web page. It's just their standalone mining page that isn't functioning at the moment.
To get the javascript you need, if you have signed up just click on "Publishers" in the left hand column from the main page. It will ask you for the domain name you are going to put it on and that's pretty much it. The Javascript is just a couple of lines.