NextGen slideshow won't load with Firefox and Opera

In Chrome console (very useful tool) there’s a jQuery error being dump and it points to a cross-domain conflict.

XMLHttpRequest cannot load https://dragesetvarehus.no/index.php?callback=json&api_key=true&format=json&method=gallery&id=1. Origin https://www.dragesetvarehus.no is not allowed by Access-Control-Allow-Origin.

Note the first http without www and the second one with it.

The gallery works in any browser if I go to https://dragesetvarehus.no

Maybe your hosting cPanel has the option to redirect the calls from www to www-less. But I’ve just found this: go to the General Settings page and remove “www” from the blog and WP URLs