"HTML7 magic" on Facebook
jasonbos.co
jasonbos.co
What's unusual to me is that the username field is on the initial page. On most sites I've used that upgrade from http to https, only a generic login button is on the unencrypted page, e.g. creditkarma.com. Maybe facebook a/b tested this setup and found users log in more often.
Also you can name a class anyway you want pretty much.