Joomla application was installed through Subscriber’s Control Panel > Applications > Joomla > Install. Configuration of site's preferences through Joomla's Administrative interface fails with error when I try to save the changes: http://domain.tld/administrator/index.php > Global Configuration > Save
Could not save data. Error: Could not write to the configuration file
PHP is runing in Apache mode in domain preferences.
According to Joomla Troubleshooting Guide:
Get your web server to run PHP as CGI or FastCGI
So change the PHP handler of the domain from Apache module to FastCGI in Plesk Control panel->domains->domain.tld->hosting preferences->PHP.