I changed all instances of https://www.flickr to https://www.flickr in the two files mentioned above (responsive-flickr-gallery/afgFlickr/afgFlickr.php and responsive-flickr-gallery/index.php) but this was not sufficient.
I then made the additional changes mentioned by Sorabi in his second post (such as (if ( !preg_match(“|https://(.*?)(/.*)|”, $url, $matches) ) { …) and that fixed the problem.
Thanks!!!