There was a problem with commenting, where users (including me) were getting 403 errors when they tried to post a comment. The problem was the WordPress Jetpack plugin. The Jetpack Comments system makes the avatar a hidden field, and my domain provider (quite wisely) does not like hidden fields, since they can be used to plant exploits on the server. And with a certain very large country currently hacking anything and everything, it’s better to be safe than sorry, so I disabled Jetpack entirely, and you can now post comments again. Sorry for the trouble!