After clicking on the preview button, it is hard to enlarge the new comment text box again, since it re-appears below the preview, and the resize corner of the new comment text box can be dragged no further down than the bottom of the screen (which likely is not very far at that point).

Ideally, the new comment text box should retain its size across the preview generation. If that should be too hard, another option could be to have the preview appear below the text box.