The Firefox 159 release date is Tuesday, October 27, 2026, according to Mozilla’s own release notes. It’s in beta now, and the changes listed so far are mostly for web developers, not everyday users.
That makes it a quieter release than Firefox 158, which switched on JPEG XL and added AI form filling. Here’s what’s confirmed, what isn’t, and how to update the moment it lands.
The short version:
- Release date: October 27, 2026
- Status today: Beta channel, with release notes still a work in progress
- Listed changes: masonry syntax removed, a Sanitizer API tweak, scoped custom element registries
- Add-on changes: none listed
Mozilla can still add notes before launch, so treat this list as a snapshot.
When is the Firefox 159 release date?
Mozilla’s developer release notes say Firefox 159 ships on October 27, 2026. PCWorld gives the same date in its Firefox 158 coverage.
The stable build rolls out to all users over the hours and days after release. If you don’t see it right away, that’s normal.
Firefox 158 only arrived on October 13, so this is a short gap. That fits Mozilla’s regular release train, where each version spends several weeks in beta before it reaches you.
What’s confirmed in Firefox 159 so far
The beta release notes list three developer-facing changes. They won’t change how Firefox looks, but they affect how some websites are built.
| Change | What it means | Who cares |
|---|---|---|
| Legacy masonry syntax removed | The old masonry grid value and masonry-auto-flow are gone. Developers should use grid lanes instead. |
Web developers testing layouts |
| Sanitizer API change | Methods like Element.setHTML() now strip unwanted elements while parsing. Output is the same, except adjacent text lands in one text node. |
Developers handling user-generated HTML |
| Scoped custom element registries | Shadow trees can have their own registry, which avoids name collisions between web components. | Web component authors |
The masonry syntax was only enabled by default in Nightly, so ordinary Firefox users never had it. That’s why this removal shouldn’t break sites you visit.
Two experimental features also appear in the notes, but they’re off by default. You’d have to flip them in about:config, so skip them unless you’re curious.
How the Firefox release train explains this update
Mozilla ships Firefox on a fixed schedule. New code moves from Nightly to Beta to the stable release, and each step gives testers time to catch bugs.
That’s why a beta page can tell you the release date with confidence. The date is set by the calendar, not by whether a feature is ready. Features that miss the cutoff simply wait for the next version.
It also means a quiet release isn’t a bad sign. Some versions carry a headline feature, and others mostly clean up behind the scenes. Firefox 159 looks like the second kind, at least from the notes published so far.
What we don’t know yet
The release notes I checked list no new user-facing features for Firefox 159. That doesn’t prove there are none. Mozilla often publishes its consumer-friendly summary on launch day.
Some reports mention Wayland improvements for Linux users, but I couldn’t verify the details from a source I could open. Until Mozilla’s official notes say so, consider that unconfirmed.
Also remember that Firefox 158’s AI form filling is “rolling out gradually,” per PCWorld. If you don’t have it yet, a new version number won’t necessarily change that.
How to update Firefox when 159 arrives
Firefox normally updates itself in the background. To check by hand, follow these steps:
- Open the menu and go to Settings, then General.
- Scroll to Firefox Updates and select Check for updates.
- Restart when prompted. Your tabs come back after the restart.
You’ll know it worked when the version number under Firefox Updates reads 159. On Linux, your package manager may deliver it a little later than Mozilla’s own build.
Why you should still install it quickly
Even quiet releases usually carry security fixes. Firefox 158 patched 77 flaws, including 30 rated high risk, according to PCWorld. We covered what else changed in Firefox 158 and JPEG XL.
I haven’t seen the security list for Firefox 159 yet, and it typically appears on release day. Check it then, but don’t wait for it before updating.
If you’re curious about the visual overhaul instead, our guide to the Firefox Nova redesign covers the settings worth checking.
Frequently Asked Questions
What is the Firefox 159 release date?
October 27, 2026, according to Mozilla’s developer release notes. The build is in beta until then.
What’s new in Firefox 159?
So far the notes list developer changes: masonry syntax removed, a Sanitizer API tweak and scoped custom element registries. No user-facing features are listed yet.
Can I try Firefox 159 before it’s released?
Yes, through the Beta channel, though betas can be less stable. Most people are better off waiting for October 27.
Will Firefox 159 break any websites?
Unlikely. The removed masonry syntax was only on by default in Nightly, so live sites shouldn’t depend on it.
My take: don’t expect fireworks from this one. It’s a maintenance-style release, and the best reason to install it is the security patching Firefox ships every cycle. Update on release day, glance at the official notes for anything user-facing, and carry on.
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