Firefox 158 is scheduled to ship on October 13, 2026, and its biggest change is that JPEG XL image support switches on by default. If you’ve never heard of JPEG XL, the short version is that it’s a newer image format that can make photos smaller without making them look worse.
Here’s what’s coming, what’s already confirmed, and what you can safely ignore.
The quick facts first:
- Release date: October 13, 2026, according to the Firefox release tracker.
- Current version: Firefox 157, with a small 157.0.1 fix released on October 6.
- Headline change: JPEG XL (
image/jxl) support is enabled by default. - Status today: Firefox 158 is in Beta, so the final list can still shift.
Mozilla’s own release notes for Firefox 158 are marked as a work in progress. Treat everything below as the plan, not a signed contract.
Why JPEG XL in Firefox 158 matters
JPEG XL is a royalty-free image format. It supports lossy and lossless compression, transparency, animation, and HDR. In plain terms, one format can replace JPEG, PNG, and GIF in many cases.
Firefox 158 also adds image/jxl to the default Accept header it sends when asking for images. That header is how a browser tells a website which formats it can handle. Sites and CDNs can now serve JXL files to Firefox users automatically.
Chrome went down the same road recently. We covered the details in our Chrome 155 JPEG XL guide. With both browsers on board, it’s much more realistic for websites to start using the format.
Why should you care? Smaller image files mean faster pages and less mobile data used. That helps most on slow connections, where a heavy photo can stall a whole article.
What else is new in the Firefox 158 update
Most other changes are aimed at web developers. A quick scan of the Beta notes shows these items:
| Change | What it does |
|---|---|
| JPEG XL on by default | Firefox can now display image/jxl files without you flipping a setting. |
calc() typed arithmetic |
Developers can divide two values with different units and get a plain number. |
WebTransport.getStats() |
Sites can read connection and datagram statistics. |
Notification navigate option |
A notification can open a specific URL when you click it. |
runtime.getVersion() |
Extensions can read their own manifest version. |
Most readers won’t notice any of these directly. They do mean web apps can get a little smarter without extra workarounds.
The notification option is the easiest to picture. Click an alert from a web app, and it can jump straight to the right page instead of just opening the site’s home screen.
What you’ll notice as a regular user
Not much at first. Image formats are invisible when they work. You’ll mostly see slightly faster page loads on sites that start serving JPEG XL, plus better-looking HDR photos where the site supports them.
The Beta notes for Firefox 158 list no browser interface changes. That’s a quiet release for the toolbar, tabs, and settings.
If you want to see the full picture, wait for the final release notes on October 13. Mozilla often fills in gaps late in the cycle.
Experimental features you can try early
Three features are in the notes but switched off by default. They only appear in Nightly builds, so they’re for tinkerers. You turn them on through about:config.
The first is corner-shape CSS, which lets designers create shapes beyond simple rounded corners. The second is on-device speech recognition for the Web Speech API on desktop, which means no cloud service is needed. The third is streaming request bodies for fetch().
The on-device speech option is the one worth watching. Keeping voice processing on your own machine is better for privacy.
How to get Firefox 158 when it lands
Firefox updates itself in the background. To check manually, open the menu, go to Settings, then General, and look under Firefox Updates. Click the update button if one is waiting.
If you’re still on an older release, update soon. The recent 157.0.1 build included a security fix, listed by Mozilla as advisory MFSA 2026-104. It also fixed failed downloads on macOS and a sidebar that could get stuck on the Bookmarks or AI Chatbot panel.
Keeping your browser current is the cheapest security upgrade you have. If you want to understand how often browsers ship these updates, our Chrome release cycle guide explains the pattern.
Frequently Asked Questions
When is Firefox 158 coming out?
The release tracker lists October 13, 2026. Dates can slip by a day or two if Mozilla finds a serious bug late.
What is JPEG XL and do I need it?
It’s a modern image format that offers smaller files and good quality. You don’t need to do anything. Firefox will just load these images when a site offers them.
Will Firefox 158 slow down my computer?
Nothing in the Beta notes suggests that. The changes are mostly under the hood and focused on web standards.
Can I test the new features before the release?
Yes. Install the Firefox Beta or Nightly channel. Keep it separate from your main profile, because pre-release builds can be unstable.
Our take
Firefox 158 isn’t a flashy release, but the JPEG XL switch is the kind of quiet change that pays off over the next year as more sites adopt the format. Update when it arrives, skip the experimental flags unless you’re curious, and don’t expect a new look. If you build websites, start testing JXL delivery now.
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