Firebase: The specified authentication provider is not enabled for this Firebase

I'm trying to set up a new Firebase web project.
I created a new user and try to log into the project.

That's my code:

    // Create a callback to handle the result of the authentication
  function authHandler(error, authData) {
    if (error) {
      console.log("Login Failed!", error);
    } else {
      console.log("Authenticated successfully with payload:", authData);
    }
  }
    // Or with an email/password combination
  var ref = new Firebase("http://ift.tt/12MJqJP");
  ref.authWithPassword({
    email    : "the@mail.com",
    password : "password"
  }, authHandler); 

Pretty standard Firebase code.
But I always get this error:

Login Failed! Error: The specified authentication provider is not enabled for this Firebase.

As you can see it's activated. What am I doing wrong?

Thank you so far :)