Holding down the enter key and clicking on comment during practice makes the screen go black.
I have noticed in the past if I do not let go of the enter key I can still make changes to my answer. So my brain is in the habit of holding it down when it has doubt. Anyway if the key is held down and I click on the comment link during the practice the screen goes all black and I have to start a new session of Duolingo. I am using Firefox 19.0. Not an important issue just interesting.