Last modified: 2012-02-23 00:56:55 UTC
Seen currently on both test.wiki and test2.wiki: The page at https://test.wikipedia.org/wiki/Special:UploadWizard displayed insecure content from http://upload.wikimedia.org/wikipedia/commons/4/42/Loading.gif.
This appears to actually be in mediawiki.feedback.js in core... $( '<img src="http://upload.wikimedia.org/wikipedia/commons/4/42/Loading.gif" />' ) As a quick fix I'll just swap it to protocol-relative, but it should be replaced with CSS and a local image.
r112169 does the protocol-relative switch
r112172 does a proper fix, turning it into a locally-hosted .gif loaded via styles in the module.