Firefox Nightly adds support for a faster, more modern web connection

Firefox Nightly 154 has picked up support for QUIC version 2, giving the browser another networking upgrade that’s mostly invisible to users, but still matters every time a webpage loads over HTTP/3. Mozilla quietly enabled the feature in the latest Nightly builds after landing the necessary changes in its networking stack.

We’ve been following Firefox Nightly pretty closely lately. Over the past few weeks, we covered Mozilla’s new gradient themes and customizable widgets, the Nova redesign that sparked mixed reactions, and even the updated Firefox logo that started appearing in Nightly builds. This latest change isn’t something you’ll spot in the UI, but it’s arguably just as important under the hood.

If terms like QUIC and HTTP/3 sound unfamiliar, here’s the basic rundown.

QUIC is the network protocol that powers HTTP/3, the newest version of the web protocol browsers use to communicate with websites. It was designed to reduce delays, recover from connection hiccups faster, and generally make browsing feel snappier, especially on unstable networks.

Until now, Firefox only supported QUIC v1. Starting with Firefox 154 Nightly, the browser can also offer QUIC v2 when establishing an HTTP/3 connection. The browser doesn’t force the newer version, though. Instead, it offers both versions during the initial handshake and lets the server decide which one to use.

Mozilla described it this way in its release note request. “Firefox offers both QUIC v1 and v2 using compatible version negotiation (RFC 9368); the server selects which version is used, so connections upgrade to QUIC v2 when the server chooses it and remain on QUIC v1 otherwise.”

That last part is actually the catch, because users won’t suddenly notice every site switching to QUIC v2 overnight. Websites and services also need to support it before the newer protocol is actually used. Mozilla even notes in the bug report that “servers must also pick v2 from the offered list for connections to actually use it.”

The company is treating this as a Nightly-only experiment for now. It also added telemetry to measure how often Firefox successfully negotiates QUIC v2 during HTTP/3 handshakes before deciding whether it’s ready for Beta and stable releases.

Mozilla has been making plenty of visible changes in Nightly recently, including a streamlined tab context menu we covered a few weeks ago. Compared to that, QUIC v2 isn’t flashy at all, but browsers spend far more time talking to servers than showing menus, so this is probably the kind of change that quietly earns its keep.

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