When trying to vote to close a question as a duplicate, I copied the link to the duplicate question and, as I use HTTPS by default, the link was rejected with an error message along the lines of "not a valid URL".
s and just using
http://... and the appropriate question was highlighted, allowing me to cast my vote.
Surely, we should be able to access all of the functionality over a secure connection?
Related feature request on the main meta: Better HTTPS support for Stack Exchange sites