To be able to click the "I'm done" button on the firsts posts queue, you need to first do something. However, the button appears the same when I've done nothing (and it should be faded out).
As you can see, the button shows as clickable but isn't. When I've upvoted the post and go to click the button, it looks the same (but gains a hover effect).
Running Firefox Quantum here on OS X El Capitan.