You're talking about the Facebook website, which is irrelevant to this discussion. If someone sends an insecure HTTP URL through Facebook chat, then Facebook h

You're talking about the Facebook website, which is irrelevant to this discussion. If someone sends an insecure HTTP URL through Facebook chat, then Facebook has to make an insecure HTTP connection to that URL in order to scan it, which leaks the URL, even if the chat session was using HTTPS.