There are some sites I go to over and over again for inspiration, to learn how to make things better for users, sites I hold up as 'this is so amazingly crafted, this is what I want to build for people'.
Mozilla's is one of them. GoG.com is another. Posterous used to be but well... Posterous spaces happened. ;)
A really cute implementation of a simple idea, although, alas, Firefox doesn't seem to think gamers exist. At least a third of the questions had no answers that were even close to what I would pick.
That being said, what I really like is the quiz UI. For radio-button style questions, it's really great! Why make the user keep clicking 'next' after checking a radio button - they can only select one darn button anyway! And the autocomplete at the end, with the option to 'Go back' is very similar to Google's 'undo'. It's a great feature because it takes the 'responsibility' away from the user, while not depriving them of choice or power. By this I mean, rather than constant alerts popping up saying, 'Make this decision, make it nao, and it's FINAL SO YOU BETTER KNOW WHAT YOU WANT AND CHOOSE CORRECTLY OR YOU WILL DIE AS IF YOU DRANK FROM THE FALSE GRAIL!!!1!1!!' ahem... it just lets you do your stuff, and gives you a way out if you change your mind.
~_o From nao on, my radio button quizzes shall be done in this seksy style!
And yes, they put all this hard work into making it all shiny and here I am raving about their quiz UI. XD What can I say.
P.S.: This wouldn't work for checkbox style questions - those require the user to select, then click next/submit, because there's no way to tell when the user is 'done'. The signal for that needs to come from the user. So alas, no shinies!