There were a number of issues with this spec:

1. The deletion of the U2F device needed an `accept_confirm` block
2. The "We heard back from your U2F device" message is shown only briefly
   before the JavaScript handler submits the form. The only way to fix this is
   to put a delay in the submission.
3. The "Remember Me" field can't be checked in step 2 for the same reason.