How to enable HTTP3 in Chrome / Firefox / Safari

Mattias recently tweeted that his website can now be served over HTTP/3 “even though no browser supports it yet”.

While it’s true that no browser supports it out of the box right now, there are options to enable HTTP/3. Here’s how.

πŸ§ͺ As with all experimental technolgy/features: things might break! Be warned!


Google Chrome

If you search chrome://flags you’ll find an option named “Experimental QUIC Protocol” which you can enable:

That alone however won’t do. You’ll also need to enable a specific HTTP3 version, apparently. This extra change cannot be done through chrome://flags, but only through a command line option.

To fully enable HTTP/3 in Chrome, you must launch it with the command line options --enable-quic --quic-version=h3-27 :

/Applications/Google\ Chrome\\ Chrome\ Canary --enable-quic --quic-version=h3-27


Set network.http.http3.enabled to true in about:config

At least Firefox 75 is required.


Safari Technology Preview Release 104 which was just released has added HTTP3 as an experimental feature. To enable it, you’ll first need to enable the “Develop” menu through its settings.

If you’re running (the unreleased) macOS 10.16 / iOS 14, you can now use the Develop menu and underneath Experimental Features enable it.

πŸ™ Thanks to Kai for digging up the fact that macOS 10.16 is required.


How to test this?

A good site to test your connection is Visit that site and open the DevTools of your browser (SHIFT+CMD+I). In the Network tab enable the protocol column and refresh the page.

Here’s an example of Firefox: is also a good site you can use. I did notice that Firefox for example sometimes loads that site using HTTP/1.1 and sometimes using HTTP/3 … experimental features, right? πŸ˜‰


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Published by Bramus!

Bramus is a frontend web developer from Belgium, working as a Chrome Developer Relations Engineer at Google. From the moment he discovered view-source at the age of 14 (way back in 1997), he fell in love with the web and has been tinkering with it ever since (more …)

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  1. > I did notice that Firefox for example sometimes loads that site using HTTP/1.1 and sometimes using HTTP/3
    75.0 (64 bits) : 1st connection HTTP1/1, then it switches to HTTP/3. Everything’s fine πŸ™‚

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