Firefox 158 rolls out today with JPEG XL switched on by default, according to Mozilla’s developer notes for the release. Until now it was off unless you went looking for it.
JPEG XL is a newer image format, an international standard from the JPEG committee. It’s royalty-free, so any browser or app can use it without paying a license fee.
What it does for you is lighter pictures. Google says JPEG XL compresses images 30 to 50% better than JPEG, so the same photo takes less data to load. It can also repack an existing JPEG into a smaller file and turn it back into the exact original later.
The other trick is progressive rendering: the picture starts drawing while it’s still downloading. Mozilla’s demo photo is 135KB, and you can tell what it shows after only a few kilobytes arrive.
Here’s what the timing hides: Chrome got there first. Google’s Chrome team wrote on October 6th that Chrome 155 ships JPEG XL decoding.
That’s the same Chrome whose team decided in 2022 to pull its experimental JPEG XL support, hidden behind a setting, arguing the format didn’t add enough over existing ones to be worth turning on. Google’s reason for the U-turn: developers kept asking, and asking.
Both browsers now build on the same decoder, jxl-rs, written entirely in the Rust programming language. Mozilla worried that the older, 100,000-line decoder gave attackers too much to aim at, and challenged Google Research to build a safer one. Google says it removes memory-safety risks (the kind of bugs that turn into security holes) from one of the most targeted parts of any browser.
Apple’s Safari has read JPEG XL since 2023, so Chrome, Firefox and Safari now all open the format.
So, smaller and sharper images for everyone? Partly. Google’s own post tells developers to try both AVIF, another modern image format, and JPEG XL, and expects JPEG XL to help most with very high-quality photos and ones that must stay pixel-for-pixel exact.
Mozilla’s own test agrees. On its fox photo, AVIF made the smaller file at medium-high quality, and JPEG XL won when nothing could be lost. That’s a recommendation to test, not a crowning.
And none of this shrinks a single web page by itself: sites have to make and serve .jxl files first. Firefox 158 helps there, because it now tells sites it accepts JPEG XL whenever it asks for an image, so a server can send it that version.
If you run a site, this is the week to test it. If you just browse, update Firefox and let the web catch up.
