Avatars are really, really, small pictures to begin with so when you enlarge them, they become blurry, but you can enlarge them a bit by holding down the "ctrl" key and clicking the plus key (shift and the = key) until its large enough to see, and not so blurry that you can't see a clear picture. To get the screen back down, just hold down the "ctrl" key plus the minus key (key to left of the = key).