Wait for the "Connecting to Persona" message to vanish.
Capybara::Persona#visible? should be able to return false.

(Previously, it'd raise.  That's just weird.)
Don't wait for signin to complete when submitting credentials.

Signin completion isn't guaranteed when submitting credentials (for
example, someone could enter the wrong password).  Also, waiting for
completion isn't a part of submission anyway.
The "remember me" dialog doesn't always appear.