Container Username Assistant by k20ali

Container Username Assistant helps you keep usernames separate between Firefox containers. Save a username for a website in one container, and the extension can fill it automatically on later visits to the same website in that container.

1. Open an HTTP or HTTPS login page in a Firefox desktop container.
2. Enter your username normally.
3. Click the extension icon and choose Add Rule or Update Rule to save the username.
4. Visit the same website in the same container later. The saved username can be filled automatically.
5. Open the options page whenever you want to review or remove saved rules.

• The extension stores only the username you explicitly choose to save, the website host, and the Firefox container identifier.
• It does not read, store, or transmit passwords.
• It does not read or write cookie values. Firefox requires the cookies permission for its contextualIdentities API, which this extension uses to identify containers.
• Saved rules use Firefox browser.storage.sync. If Add-ons synchronization is enabled in Firefox desktop Sync settings, rules may be synchronized through your Mozilla account.
• The developer does not operate a backend server and does not receive your saved rules.
• No advertisements, analytics, tracking beacons, or remotely loaded code are included.

This release supports Firefox desktop 140 or later. Firefox for Android is not supported.


Container Username Assistant is an independently maintained fork of Account Per Container, with improvements to rule persistence, login-field detection, URL and tab validation, and reliability. It is not affiliated with the original author.