Got it working on 4.1…

Open phpFlickr.php and change the following lines:

var $rest_endpoint = 'https://api.flickr.com/services/rest/';
 var $upload_endpoint = 'https://api.flickr.com/services/upload/';
 var $replace_endpoint = 'https://api.flickr.com/services/replace/';

To:

var $rest_endpoint = 'https://api.flickr.com/services/rest/';
 var $upload_endpoint = 'https://api.flickr.com/services/upload/';
 var $replace_endpoint = 'https://api.flickr.com/services/replace/';

Then add the following code to flickr-gallery.php, just before the “add_shortcode(‘flickr’…” line:

if (shortcode_exists('flickr')) {
    remove_shortcode('flickr');
}

More on my website.