Slickr Flickr 2.x has been updated to use HTTPS for connecting to Flickr in line with the Flickr’s new requirements for more secure access
You do not need to do anything other than upgrade to the latest version of Slickr Flickr.
Possible SSL Error
However if after upgrading you get the following error you will need to get your host to unblock your site’s access to Flickr.
Error fetching Flickr photos: WP HTTP Error: SSL read: error:00000000:lib(0):func(0):reason(0), errno 0
This indicates your host is blocking the Outbound HTTPS connection to Flickr. This might be a firewall issue or might be due to a bug in CURL. In either case you need your host to sort this out.
When you connect to the Flickr feed over HTTPS in your browser by clicking the link you are connecting from your desktop/laptop DIRECTLY to Flickr and hence it works fine but when Slickr Flickr connects from your website to the Flickr feed over HTTPS it is your WEBSITE that is connecting to Flickr and it is the host that is blocking the connection.
To resolve this you need to get your host to allow your website to connect to api.flickr.com over HTTPS.
Your host may just need to add api.flickr.com to a firewall “Whitelist” or may need to take some other action such as allowing OUTBOUND connections on PORT 443 to allow your website to connect to Flickr. Or they may need to update the cURL library.
For more on this please see http://wordpress.org/support/topic/ssl-error-with-latest-update