HTTP only onion services are marked as insecure in TBB ff52 nightly
Go to the onion service of torproject.org: http://expyuzz4wqqyqhjn.onion/
Click on the (i) icon in the left of expyuzz4wqqyqhjn.onion, this should appear:
Connection is Not Secure
Clicking further on ">":
Your connection to the site is not private. Information you submit could be viewed by others (like passwords, messages, credit cards, etc.)
Trac:
Username: blockflare