Does Firefox Support JPEG XL?
Yes — since Firefox 158, released on 13 October 2026. It's on by default, on every platform, using a decoder written in Rust. Older versions, the ESR builds companies use and several forks are a different story. Here's which Firefox you have and what to do about it.
by Robert Castillo · Published
The short answer
Yes. Firefox 158, released on 13 October 2026, shows JPEG XL images out of the box. Its release notes put it in one line: Firefox now supports the JPEG XL image format. There is nothing to install and nothing to switch on — a .jxl image on a web page simply appears, like a JPEG or a WebP.
Technically, the whole change is one preference, image.jxl.enabled, which now defaults to true (bug 2065096). Mozilla announced it for all platforms, Android included. The decoder doing the work is jxl-rs 0.7.4, written in Rust — the same family of code that Chrome switched on exactly a week earlier, in Chrome 155.
The catch is every Firefox that isn't 158 or newer. Older releases, the Extended Support Releases that companies roll out, and several popular forks still ship with JPEG XL switched off — or without the decoder at all. The table below sorts that out.
Which Firefox do you have?
Here is every Firefox you're likely to meet in October 2026, and what each one does with a .jxl image.
| Firefox build | JPEG XL | What to do |
|---|---|---|
| Firefox 158 and later | On by default | Nothing |
| Beta / Developer Edition 159 | On by default | Nothing |
| Nightly 160 | On (since Nightly 153) | Nothing |
| Firefox 152 to 157 | Built in, off | Update, or tick it in Firefox Labs |
| Firefox ESR 153 | Built in, off | image.jxl.enabled → true |
| ESR 140, ESR 115, Firefox 151 and older | No decoder | No setting helps: use a viewer or convert |
| Firefox for Android 158 | On by default | Nothing |
| Firefox for iPhone and iPad | Yes, through Apple's engine | Needs iOS 17 or later |
Firefox on iPhone is the exception that proves the rule: it is built on Apple's WebKit engine, not on Firefox's own, so it shows JPEG XL whenever Safari does — on iOS 17 and later — whatever its version number says.
To see which one you have, open the menu ☰ → Help → About Firefox (on a Mac, Firefox → About Firefox). The same window downloads the update, which is the simplest fix for most of the rows marked as off.
How to switch it on in an older Firefox
If you can't update — a work laptop pinned to ESR 153, or a fork that hasn't caught up yet — you can still turn the decoder on, as long as your build includes it. That is true of Firefox 152 to 157 and of ESR 153. It is not true of ESR 140, ESR 115 or anything before 152.
Option 1 — Firefox Labs (Firefox 152 to 157)
Open Settings, choose Firefox Labs in the side menu and tick Media: JPEG XL. Mozilla deliberately keeps that label in English in every language, so look for exactly those words. Since Firefox 146, Labs works even if you've switched off telemetry and studies.
Option 2 — about:config (any build with the decoder)
Type about:config into the address bar and accept the warning. Search for image.jxl.enabled and double-click the row until the value reads true. This is the same switch Labs flips, and it works on ESR 153 too.
Reload and check
Reload the page you were on, or run our browser test, which asks your browser to draw three tiny JPEG XL images and tells you whether it managed. If it still says no, restart Firefox once.
If image.jxl.enabled is missing, or flipping it changes nothing, your copy was built without the decoder. Until Firefox 152, JPEG XL was only ever compiled into Nightly, so on ESR 140 the preference exists but is a switch connected to nothing. No setting fixes that; only a newer Firefox does — or, for a one-off file, our viewer, which decodes JPEG XL by itself and works in any version.
How Firefox got here
2021 — Nightly only
Firefox 90 added a decoder built on libjxl, the C++ reference library, behind image.jxl.enabled. It was compiled into Nightly alone, so the preference did nothing in normal Firefox for five years.
Neutral, not negative
Mozilla's official position on the format was — and on paper still is — neutral: useful features, but not enough to justify another C++ image decoder. A memory-safe one, it added, would cut that cost considerably.
Sept 2024 — the Rust condition
Mozilla said the reference decoder was over 100,000 lines of multithreaded C++, and that if Google Research delivered a safe, fast Rust decoder meeting its production bar, it would ship it. That decoder became jxl-rs.
June 2026 — Firefox 152
The Rust decoder was built into Beta and Release for the first time, switched off, with a checkbox in Firefox Labs. Nightly turned it on by default from version 153.
Aug–Sept 2026 — intent to ship
On 24 August Mozilla announced JPEG XL on by default for Firefox 157; Chrome filed its own intent the same morning. On 3 September the target moved to 158 because the remaining work took longer than estimated.
13 Oct 2026 — on for everyone
Firefox 158 shipped with the preference on by default. With Chrome 155 a week earlier and Safari since 2023, the three big engines all show JPEG XL.
What Firefox's JPEG XL does — and what it doesn't
Progressive loading works. A JPEG XL file can be drawn while it is still downloading, starting blurry and sharpening as the data arrives, and Mozilla pushed for it in the Rust decoder. In Mozilla's own write-up, a 135 kB photo of a fox is recognisable after only a few kilobytes. Safari, which has had JPEG XL since 2023, doesn't render it progressively.
HDR is shown as SDR. Mozilla's intent to ship says it plainly: HDR JPEG XL images display in standard dynamic range, as Firefox currently does with every image format, although with better tone mapping than the other formats get.
Speed is close, not identical. In Mozilla's benchmark over five formats, run on the engineer's own machine, Firefox's JPEG XL decoding came out slightly ahead of Safari's, which uses the C++ libjxl. Against Firefox's other image decoders it was close on large images and further behind on small ones. Decoding is spread over several threads; a hidden preference, image.jxl.decode_participants, sets how many, and its default of 0 means automatic — between 2 and 8 depending on your processor.
It reads JPEG XL; it doesn't write it. jxl-rs is a decoder only, so Firefox can show a .jxl but not save one. With the preference on, Firefox also tells websites it understands the format, adding image/jxl to the Accept header it sends for images, and it treats downloaded .jxl files as something it can open in a tab itself. To create JPEG XL files you still need an encoder — ours runs in the browser.
Firefox forks: which ones show JPEG XL
Forks follow Firefox's code but not always its calendar, so the answer depends on which version they're built on and whether they override Firefox's default. We checked each one in its own source code or official release notes on 15 October 2026, not in forum threads, which still repeat claims from years ago.
| Browser (version checked) | JPEG XL | Why |
|---|---|---|
| Waterfox 6.7.6 (13 Oct 2026) | On | Built on Firefox ESR 153, but Waterfox sets image.jxl.enabled to true itself and backports jxl-rs 0.7.4 |
| LibreWolf 158.0-1 (13 Oct 2026) | On | Built on Firefox 158 and inherits its new default; LibreWolf's settings don't touch it |
| Floorp 12.20.1 (9 Oct 2026) | Off | Built on Firefox 157.0.1: the decoder is there, switch it on in about:config |
| Zen 1.23.2b (9 Oct 2026) | Off | Built on Firefox 157.0.1: on once it moves to 158, about:config meanwhile |
| Pale Moon 35.0.2 (6 Oct 2026) | On | Its own engine, born from an old Firefox; JPEG-XL since 31.4.0 (November 2022), using libjxl |
The rule of thumb: a fork built on Firefox 158 or later gets JPEG XL automatically unless it switches it off, and one built on Firefox 152 to 157 or on ESR 153 has the decoder but needs image.jxl.enabled set to true. Pale Moon is the odd one out — it left Firefox's code base years ago, added its own JPEG-XL support in 2022 and has kept it on since. Zen's development branch already targets Firefox 158, so its next release should change that row.
Firefox 158 and still no JPEG XL?
Confirm the version
Check About Firefox says 158 or later. Forks show their own version number, so for them look up which Firefox they're built on — Zen 1.23 and Floorp 12.20 are still on 157.
Check the switch hasn't been turned off
In about:config, search for image.jxl.enabled. If it reads false in bold, something changed it: a privacy-hardening user.js, an old tweak, a sync from another machine. The reset arrow at the end of the row puts the default back.
Look for a padlock
On a company computer, a policy can lock preferences. A padlock icon next to the row means only whoever manages the machine can change it.
Test the browser, not the site
Run the browser test. If it says yes, Firefox is fine and the problem is the image or the website: a file that isn't really JPEG XL despite its name, for instance, or a site that sends Firefox a different format.
FAQ
Does Firefox support JPEG XL now?
Where is the JPEG XL setting in Firefox?
about:config, under image.jxl.enabled. In Firefox 152 to 157 the same switch also appears in Settings → Firefox Labs as Media: JPEG XL. In Firefox 158 you shouldn't need either: it's already on.Why did Firefox take so long?
Does Firefox for Android support JPEG XL?
Can Firefox save or convert images to JPEG XL?
.jxl files. To make one, use a converter such as JPG to JXL, which runs in your browser without uploading anything.