Happy-Eyeballs on Max Inden

Talk "A Report on Firefox's HEv3 Implementation" @IETF 126

Mon, 20 Jul 2026 00:00:00 +0000

I reported on Firefox’s Happy Eyeballs v3 implementation in the HAPPY working group at IETF 126 in Vienna.

Happy Eyeballs v3 races connection attempts across address families and protocols and keeps the first one that connects. Since IETF 125 it is enabled by default in Firefox Nightly, reaching roughly 15k users.

The implementation is a library of its own, mozilla/happy-eyeballs: a deterministic, sans-I/O state machine in Rust with no network and no clock. The caller drives the I/O and passes time in. It does not depend on Firefox, it embeds in Necko’s C++ event loop, and every scenario is a plain unit test.

Talk "Happy Eyeballs v3 in Firefox" @IETF 125

Wed, 18 Mar 2026 00:00:00 +0000

I presented Firefox’s Happy Eyeballs v3 implementation in the HAPPY working group at IETF 125 in Shenzhen.

At that point the implementation had landed in Firefox Nightly, still off by default and reachable by flipping network.http.happy_eyeballs_enabled in about:config. It followed the draft with no major deviation.

I introduced mozilla/happy-eyeballs, the Rust library behind it: deterministic, free of side effects, abstract over I/O and time, and with no dependency on Firefox. Each scenario is a plain unit test, which makes the algorithm easy to formalize. I offered those tests to the working group as a way to pin the algorithm down.