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Mozilla released Firefox 139.0 to the stable channel a moment ago. The new major version of the open source web browser includes several new features and improvements, as well as security and bug fixes.

Firefox 128.11.0 ESR and Firefox 115.24.0 ESR are also released today. The two Extended Support Release versions of Firefox fix security issues and bugs.

Firefox 139: the major changes and new features

Custom Wallpapers and Colors on New Tab page

Firefox users who upgrade to Firefox 139 or install the browser anew get new customization options for the browser's new tab page.

The main addition is the ability to upload any image to set it as the wallpaper on the new tab page.

The feature is rolling out over time, but you can enable it right away in Firefox Labs. This is done by loading about:preferences#experimental in the Firefox address bar and checking the "Choose a custom wallpaper or color" box on the page.

Open a new tab page afterwards and active the customize option. There you should see the new color "upload an image" option.

Translation of extension pages

Firefox's built-in translate feature supports internal pages by extensions as well now. These start with moz-extension:// and are often used to display information or settings.

This option may help Firefox users who install extensions that are only provided in languages that they may not speak or understand (fully).

Link Previews

Link Previews is another new feature that is rolling out in Firefox 139. It displays information about links before opening the linked resource directly.

To use it, you simply hold down the Shift-key and the Alt-key before hovering over a link in Firefox. Firefox displays a thumbnail, the title and a short description of the linked resource in an overlay in the browser window.

You may also get a bullet list of key points, which is created via machine learning and artificial intelligence locally.

Note that Mozilla is rolling out the Link Previews feature and limiting access to the key points feature. You can enable both right away, here is how you do that:

1. Open about:config in the Firefox address bar.
2. Accept the risk to continue.
3. Search for browser.ml.linkPreview.enabled.
4. Set the value to True to enable the Link Previews feature.
5. Search for browser.ml.linkPreview.noKeyPointsRegions.
6. Edit the string by removing your country local, e.g., DE or FR, from the string.
7. Restart Firefox.

Other changes and fixes

• The Review Checker feature is shutting down. It will stop working after June 10, 2025.
• Imports from Google Chrome, specifically payment methods and passwords, are not supported directly anymore as Google changed the way Chrome encrypts user data on Windows.  Mozilla recommends exporting passwords to a CSV file and then importing them into Firefox.
• PNG images with transparency now keep their transparency when pasted into Firefox.
• The upload performance of HTTP/3 has been significantly improved, particularly on resumed connections (QUIC 0-RTT) and high-bandwidth and high-delay connections.

Developer changes

• The hidden=until-found HTML attribute and the beforematch event are now supported.
• The Temporal API is now supported, this aims to simplify working with dates and times in various scenarios.
• The requestClose() method of the HTMLDialogElement interface is now supported.
• The largeBlob and credProps Web Authentication extensions are now supported, while the prf extension is supported on all desktop platforms.
• Based on user requests from both Mozilla Connect and Stack Overflow, the filter setting in the Network panel is now preserved across DevTools Toolbox sessions.
• The Debugger's directory root is now scoped to the specific domain where it was set.
• Timer throttling for Workers is now supported.
• Added support for the WebAuthn largeBlob extension.

Enterprise changes

• Extensions installed via policy can now enable or disable other extensions.
• The SearchEngines policy is now available on all versions of Firefox (not just the ESR).

Security updates / fixes

Firefox 139 fixes a total of ten security issues in the browser. The aggregate severity rating is critical, but Mozilla does not mention exploits in the wild. Some of the issues were found during hardening scans of the Firefox code.

You can check out the full list here.

Firefox 139.0 download and update

Most non-managed Firefox installations will be updated automatically in the coming hours and days. You can speed this up on the desktop by going to Menu > Help > About Firefox.

Downloads are also provided on Mozilla's official website.

• Firefox Beta download
• Nightly download
• Firefox ESR download

Outlook

Firefox 140 will be released on June 24, 2025. It will also be the next Extended Support Release base and replace Firefox 128.x ESR in the coming months.

Additional information / resources

• Firefox 139 release notes
• Firefox 128.11.0 ESR release notes
• Firefox 115.24.0 ESR release notes
• Firefox 139 for Developers
• Firefox 138 for Enterprise
• Firefox Security Advisories
• Firefox Release Schedule

Closing Words

Firefox 139 is a lighter release, but it still introduces a few new or improved features. Firefox users may now customize the new tab page to their liking and use the new Link Previews feature, if they want to.

Mozilla introduced a number of major additions to Firefox in the past couple of releases. Major additions were the new Profiles Manager, vertical tabs, and support for tab groups.

Now You: have you tried Firefox 139 or one of the latest versions already? What is your take on the new feature sthat Mozilla added? Feel free to leave a comment down below.