Firefox:Password Manager Debugging

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The password manager in Firefox includes the ability to log debugging information to the Browser Console, which can be enabled to help diagnose problems. This logging is off by default. Passwords are not shown in the output.

Enable Debug Logging

  1. Enter "about:config" in the URL bar.
  2. You may see a warning screen, cautioning you about changing advanced preferences. Click the button to ignore the warning.
  3. Find the signon.debug and javascript.options.showInConsole settings, and set them to true (the latter may already be true). You can enter the name in the "Filter" box at the top of the page to help find them. To change the value of a setting, right-click on the line and select "Toggle" or just double-click the line.
  4. Restart the browser. Some logging is only enabled after the restart.

View the Logging

  1. To view the logging, open the Browser Console from the Tools → Web Developer menu.
  2. Make sure the "JS" logging options are all enabled in the Browser Console.
  3. Load a web page in in the browser. You should see messages in the Browser Console like:
Login Manager (content): onFormPassword for
Login Manager: Counting logins matching host:, formSubmitURL:  httpRealm: null

To copy messages, select the text and copy the usual way e.g. choose Copy from the context menu.

Common Problems

Won't auto-fill a saved password

Note that auto-fill refers to the field being filled automatically whereas autocomplete refers to completing the field value based on what you have typed so far (usually via the autocomplete dropdown).

  • Some sites use autocomplete="off" in their HTML, which directs the password manager not to autofill/autocomplete the login on page load. You can look for this in the page's HTML, or by using the password manager logging. You may still be able to autofill the password using the autocomplete dropdown on the username field (if one exists). Here's some example output:
PwMgr mozStorage: _findLogins: returning 1 logins
Login Manager (content): found 1 matching logins.
Login Manager (content): form not filled, has autocomplete=off
Login Manager (content): autocomplete=off but form can be filled; notified observers
  • Passwords are not auto-filled in Private Browsing mode. You should still be able to autocomplete the password from the autocomplete dropdown on the username field (if one exists).
  • If there are multiple username+password combos saved for a domain and the username field wasn't pre-filled by the website, Firefox won't know which username/password to use and thus won't auto-fill. Use the autocomplete dropdown to choose the username you would like to use.
  • If the page pre-fills the username field e.g. using your session or local cookies, Firefox won't fill in the password for a different username.

HTTP Authentication popup not filled in

This is often due to the HTTP "Realm" being different from the stored login. The values the password manager is checking can be seen in the logging. Here's some example output from a successful sign in:

Pwmgr Prompter: ===== promptAuth called =====
Login Manager: Searching for logins matching host:, formSubmitURL: null, httpRealm: Mozilla Corporation - LDAP Login
Login Manager: Checking if logins to can be saved.
Pwmgr Prompter: Login unchanged, no further action needed.