Firefox Autofill Security for Credit Cards and Addresses

This article provides an overview of the security measures Mozilla Firefox uses to protect your saved credit card numbers and billing addresses. It covers how Firefox utilizes device-level authentication, local encryption, the Primary Password feature, the omission of CVV codes, and end-to-end encryption to ensure your sensitive financial and personal data remains secure from unauthorized access both locally and across synced devices.

Operating System Encryption and Authentication

Firefox never stores your credit card numbers in plain text. Instead, it encrypts this financial data on your device's hard drive using your operating system’s native security management—such as the Data Protection API (DPAPI) on Windows or Keychain on macOS.

To prevent unauthorized use by someone who gains physical access to your open browser, Firefox requires operating system authentication. Before the browser will autofill a credit card on a checkout page or allow you to view or edit the full card number in the settings menu, you must verify your identity using your computer's login method, such as a Windows PIN, OS password, Windows Hello, or macOS Touch ID.

The Primary Password Feature

If you do not want to rely solely on your operating system's login credentials, Firefox offers a built-in feature called the Primary Password (formerly known as the Master Password). When you create a Primary Password, Firefox uses it to cryptographically lock your saved credit cards and logins. When this feature is active, Firefox overrides the operating system prompt and instead requires you to enter your unique Primary Password once per browser session before it will unlock and autofill your credit card details.

Mandatory Exclusion of CVV Codes

As a strict security precaution, Firefox does not save your credit card's security code—commonly known as the CVV or CVC. When you use autofill at a checkout screen, Firefox will populate your cardholder name, card number, and expiration date, but you must manually type in the CVV. This ensures that even if a malicious actor bypasses your local security, they cannot easily complete transactions on the vast majority of merchant websites that require CVV verification.

Local Protection for Billing Addresses

Firefox separates billing addresses from credit card data because addresses do not carry the same immediate financial risk. Saved addresses are stored locally inside your specific Firefox user profile folder rather than being locked behind the Primary Password or OS-level biometric prompts. The security of your saved billing addresses relies on your computer’s user account permissions and full-disk encryption (like BitLocker or FileVault). As long as your operating system's user account is password-protected, unauthorized users cannot access the local profile files where your address data resides.

End-to-End Encryption with Firefox Sync

If you use a Mozilla account to sync your autofill data across multiple desktop and mobile devices, both your credit card numbers and your billing addresses are protected by end-to-end encryption. Before your autofill data ever leaves your computer, Firefox encrypts it locally using a cryptographic key derived from your Mozilla account password. The data travels across the internet and rests on Mozilla's servers in an unreadable, encrypted state. Because Mozilla does not have access to your decryption key, only your authorized devices can unlock and read your synced credit cards and billing addresses.