Firefox 158 is rolling out now, and its headline change is a Smart Window that can suggest form entries pulled from your open tabs and saved autofill data, according to the Firefox 158 release notes. The same release adds JPEG XL image support and patches 77 security vulnerabilities.
If you have stayed on Firefox through the AI debate, this is the version where the assistant starts touching something you do every day: filling out boxes. Mozilla says the form feature is a progressive rollout, so you may not see it yet.
TL;DR: Firefox 158 reached Release channel users on October 13, 2026 with Smart Window form suggestions, JPEG XL image support, more New Tab wallpapers and three new translation languages. It also fixes 77 vulnerabilities, 30 of them rated high. Nothing here is urgent drama, but the security patches alone are a reason to update this week.
What Firefox 158 changes for everyday browsing
Mozilla began offering Firefox 158 to Release channel users on October 13, 2026, following Firefox 157. Most items on the list are small on their own, but together they touch forms, images, PDFs, scrolling and the New Tab page.
| Change | What the release notes say |
|---|---|
| Smart Window form filling | Suggests data from relevant open tabs and saved autofill data |
| JPEG XL | Firefox can now open JPEG XL images |
| Accessible PDFs | Saving as PDF and printing on Linux and macOS produce more accessible files |
| New Tab wallpapers | A library of custom wallpapers is kept under “Your images” |
| Translation | Albanian, Belarusian and Filipino added |
| Scrolling | Scroll positions no longer rounded to whole screen pixels |
Smart Window form filling and what it can see
When you click a form field or choose Fill, Smart Window suggests data from your relevant open tabs and your saved autofill data. Picture booking a flight with the confirmation email open in another tab: the idea appears to be that the name, dates or address you need are already one tab away.
Smart Window is an optional window type with a built-in AI assistant, and it requires a Mozilla account sign-in. Mozilla’s Smart Window support page calls it an early beta, available first in the United States and Canada, with France added starting in Firefox 155.
That page says the assistant cannot reach Private Window activity, passwords, payment information or files on your device. It also says chat requests go to Mozilla’s servers and then to an AI model provider, and that neither stores chat data.
The same page says Smart Window cannot fill out forms, so the exact line between suggesting and filling is something to watch when the feature reaches you. That line is the detail most coverage will skip. If you would rather not see any of it, Settings, then AI Controls, lets you set Smart Window to Blocked.
JPEG XL support in Firefox arrives ahead of the websites
Firefox can now open JPEG XL images, a format the release notes say generally compresses better than WebP, JPEG, PNG and GIF. Chrome added its own decoder recently, which we covered in our Chrome 155 JPEG XL breakdown.
The payoff is slow, though. A site has to serve JPEG XL files before you see any difference, and most will keep using older formats until support is broad enough to feel safe. A .jxl image you open directly is the case most likely to feel different today.
Security fixes and the smaller changes
The Mozilla Foundation Security Advisory 2026-106 lists 77 CVEs fixed in Firefox 158: 30 rated high, 33 moderate and 14 low. A high rating describes potential impact, not proof that anyone has exploited the bug.
Smaller fixes include a crash while loading website icons and better readability for menus under Windows High Contrast themes. Scrolling is also smoother in a way you may feel without naming it, especially on high resolution displays or zoomed pages.
Developers get CSS calc() with typed arithmetic, a navigate option for notifications, and WebAuthn conditional UI on inputs marked autocomplete=”webauthn” alone.
Who should update this week
Firefox normally updates itself, so most people only need to restart when it asks. If you keep the browser open for weeks, restart it and check the version number under About Firefox.
Mozilla moved Firefox to a two week release cycle with Firefox 155 on September 1, 2026, according to a developer mailing list post from Sylvestre Ledru. That cadence is why version numbers keep climbing quickly, and Mozilla said it would monitor the change and adjust if needed.
If you are still deciding whether Firefox deserves to be your default, our browser comparison for 2026 is a useful companion to this release.
