UPDATE :

Freebitco.in has now added the functionality to use your browser to mine Bitcoins.

Bitopia is of the opinion that they Freebitco.in isn't actually mining Bitcoins as the difficulty in seeing actual profit from competing in Bitcoin mining is simply too large. It is more likely that they are mining alt-coins.

Not like that is of any matter to anyone using the browser miners. As long as you see a return.