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Firefox’s Password Manager can expose usernames and passwords on websites with cross-site forms (that is, HTML forms that submit to other domains). This includes many sites that will display unsanitized user-submitted content, such as MySpace.

As an initial defense against such attacks, this preference was created to prevent the Password Manager from auto-filling form fields with usernames and passwords.

Possible values and their effects


Automatically fill sign-in forms with known usernames and passwords on appropriate sites. (Default)


Do not automatically fill sign-in forms with known usernames and passwords; instead, act as though there are multiple usernames/password pairs remembered for the form (fill password after username has been manually typed).


  • This preference is named signon.autofillForms in trunk builds, but it is likely that it will be renamed to signon.prefillForms in the near future.

Recommended settings

If you use the Password Manager in Firefox to store your passwords, setting this preference to false will prevent the mentioned attack from succeeding.

First checked in

2006-12-04 by Mike Connor

Has an effect in

  • Mozilla Firefox (nightly branch builds since 2006-12-04; and above; and above)

Related bugs

Related preferences

External links