This is causing me (and my users) a lot of trouble and since I confirmed that in earlier versions of Moodle the enlarged editor window got activated even in Mozilla or Firefox, I filed this as a bug.
Text editors
Full-screen window not focused on in Mozilla & Firefox
ការពិភាក្សាត្រូវបានបិទ ដូច្នេះអ្នកមិនអាចឆ្លើយតបទៀតទេ។