If you want integrate mentions with this plugin you must edit file static/js/fbcomments.js

line 5472 change
$textarea.val(self.val());
                self.$textarea.trigger('keypress', e);

to

//$textarea.val(self.val());
                self.$textarea.trigger('keypress', e);

line 5486 change

self.updateBodyPadding(editorDiv);
 e.stopImmediatePropagation();

to

self.updateBodyPadding(editorDiv);
            //e.stopImmediatePropagation();