How does the the browser decide which form fields are username/password?

Question

Modern browsers save passwords. Which criteria affect this decision?

Background:

I have a registration page with the following form:

    <form action="/BlaBla/Account/Register" method="post">
    <div>
        <fieldset>
            <legend>Account Information</legend>
            <p>
                <label for="username">
                    Username:</label>
                <input id="username" name="username" type="text" value="" />
            </p>
            <p>
                <label for="email">
                    Email:</label>
                <input id="email" name="email" type="text" value="" />
            </p>
            <p>
                <label for="invitationCode">
                    Invitation Code:</label>
                <input id="invitationCode" name="invitationCode" type="text" value="" />
            </p>
            <p>
                <label for="securityQuestion">
                    Security question:</label>
                <input id="securityQuestion" name="securityQuestion" type="text" value="" />
            </p>
            <p>
                <label for="securityAnswer">
                    Security answer:</label>
                <input id="securityAnswer" name="securityAnswer" type="text" value="" />
            </p>
            <p>
                <label for="password">
                    Password:</label>
                <input id="password" name="password" type="password" />
            </p>
            <p>
                <label for="confirmPassword">
                    Confirm password:</label>
                <input id="confirmPassword" name="confirmPassword" type="password" />
            </p>
            <p class="buttons">
                <input type="submit" value="Register" />
            </p>
        </fieldset>
    </div>
    </form>

Mozilla seems to think that the fields securityAnswer and password are the user/pw fields, with awkward consequences (security answer stored as username is bad).

Answer 1

I'd guess it assumes the field above 'password' is the username. You could try re-ordering them.