[Plugin: WP DS FAQ] Failed to edit question

Finally found the root of the problem.

My wp-admin is working via HTTPS. When I try to edit or delete questions in

wp-admin / Settings / DS_FAQ

I get the ‘Ajax Error 5’ mentioned above, and the following line being logged to JS console:

XMLHttpRequest cannot load http://foo.bar/wp-content/plugins/wp-ds-faq/ajax.php. Origin https://foo.bar is not allowed by Access-Control-Allow-Origin.

This thread on StackOverflow has some details, I won’t copy them here, just go and read there if interested.

The fix is very simple. My modifications of wp-content/plugins/wp-ds-faq/ajax.php are below.

Before:

<?php
require_once(preg_replace('|wp-content.*$|','', __FILE__) . 'wp-config.php');

header('Content-type: text/javascript; charset='.get_settings('blog_charset'), true);
header('Cache-control: max-age=2600000, must-revalidate', true);

function error(){ die( "alert('Что-то не заработало :(')" ); }

/* ... */

After:

<?php
require_once(preg_replace('|wp-content.*$|','', __FILE__) . 'wp-config.php');

header('Content-type: text/javascript; charset='.get_settings('blog_charset'), true);
header('Cache-control: max-age=2600000, must-revalidate', true);
header('Access-Control-Allow-Origin: '.get_site_url());
header('Access-Control-Allow-Origin: '.str_replace('http://', 'https://', get_site_url()));

function error(){ die( "alert('Что-то не заработало :(')" ); }

/* ... */

Two header('Access-Control-Allow-Origin') lines added, that’s it.

Enjoy.