Original bug title:
When uploading from Flickr, unencrypted XHRs are sent from client to Flickr despite being on https://
(specifically to http://api.flickr.com/services/rest/?)
I think this will be a real issue after Firefox prompts by default when attempt to connect to http while being on https.
I read about the issues with the proxy which can't fetch the images from HTTPS (Bug 42468). If required, you'll have to set up just another proxy forwarding the API requests from the client to flickr's http API:
client <<-- encrypted traffic -->> proxy <<-- unencrypted traffic -->> flickr API
The proposed procedure would also enable you to hide the API - key.