Backward-Compatibility FIDO U2F support shipping soon in Firefox

Web Authentication (WebAuthn), a recent web standard blending public-key cryptography into website logins, is our best technical response to credential phishing. That’s why we’ve championed it as a technology. The FIDO U2F API is the spiritual ancestor of WebAuthn; to-date, it’s still much more commonly used. Firefox has had experimental support for the Javascript FIDO U2F API since version 57, as it was used to validate our Web Authentication implementation that then shipped in Firefox 60. Both technologies can help secure the logins of millions of users already in possession of FIDO U2F USB tokens.

We encourage the adoption of Web Authentication rather than the FIDO U2F API. However, some large web properties are encountering difficulty migrating: WebAuthn works with security credentials produced by the FIDO U2F API. However, WebAuthn-produced credentials cannot be used with the FIDO U2F API. For the entities affected, this could lead to poor user experiences and inhibit overall adoption of this critical technology.

To smooth out this migration, after discussion on the mailing list, we have decided to enable our support for the FIDO U2F API by default for all Firefox users. It’s enabled now in Firefox Nightly 68, and we plan for it to be uplifted into Firefox Beta 67 in the coming week.

Enabling FIDO U2F API in Firefox

A FIDO U2F API demo website being activated

Firefox’s implementation of the FIDO U2F API accommodates only the common cases of the specification; for details, see the mailing list discussion. For those who are interested in using FIDO U2F API before they update to version 68, Firefox power users have successfully utilized the FIDO U2F API by enabling the “security.webauth.u2fpreference in about:config since Quantum shipped in 2017.

Currently, the places where Firefox’s implementation is incomplete are expected to remain so.  With the increase of using biometric mechanisms such as face recognition or fingerprints in devices, we are focusing our support on WebAuthn. It provides a sophisticated level of authentication and cryptography that will protect Firefox users.

The future of anti-phishing is Web Authentication

It’s important that the Web move to Web Authentication rather than building new capabilities with the deprecated, legacy FIDO U2F API. Now a published Recommendation at the W3C, Web Authentication has support for many more use cases than the legacy technology, and a much more robustly-examined browser security story.

Ultimately, it’s most important that Firefox users be able to protect their accounts with the strongest protections possible. We believe the strongest  to be Web Authentication, as it has improved usability via platform authenticators, capabilities for “passwordless” logins, and more advanced security keys and tokens.