So I found this game demo made by firefox, and to be hones, I was sceptical. However!
It's actually pretty fun! It's really simple, you just walk around, kill things, get better armor and weapons, and then you're done.

As I said, it is still a demo. which is sad, cause I was actually enjoying it a lot.
I guess you could somewhat compare it to an extreme simple version of Diablo, cause you walk and do stuff simply by clicking on it. I guess.

It's definetley worth trying out, and I can't wait for the full game to launch. Oh, and its allso MMO, but the most people I've seen at once is 20 I think. No group system, but you see them walk around, and you can talk to them.

Link; http://www.stumbleupon.com/su/1gT3hS/browserquest.mozilla.org/