Firefox 140 ships with Unload Tab feature and new ESR base

Mozilla plans to release Firefox 140.0 to the Stable channel on June 24th, 2025. The new version of Firefox includes several usability improvements and new features, such as a new option to unload tabs to free up memory, improved vertical tab pinned tabs, faster full-page translations, and much more.

All other channels and versions of Firefox will also be updated around the same time. The Firefox ESR (Extended Support Release) versions are updated to 115.25.0, 128.12 ESR and 140.0 ESR respectively. Firefox 140 ESR is a new base for the extended support releases and it will replace 128.x soon. Firefox 115.25.0 ESR is still maintained for earlier operating system versions.

Last but not least, the development channels Firefox Beta, Firefox Developer Edition, and Firefox Nightly also move up a version to Firefox 141 and Firefox 142 respectively.

You can check out my review of Firefox 139 here.

Firefox 140: the major changes and new features

Tab Unload

The new feature is designed to free up memory while Firefox is running. Just right-click on any open tab in the Firefox web browser and select the new "unload tab" option from the context menu.

The tab remains visible but Firefox unloads it to free up memory. Unloaded tabs show up with gray icons to indicate that they are sleeping and not active.

The feature can be useful in some situations, for instance when the device is low on memory or when a website is "misbehaving" and consuming way too much memory or CPU.

Simpler to add custom search engines

Adding a custom search engine is now much simpler in Firefox. All you have to do is right-click on a search field and select the "add search engine context menu option and then the "add search engine" button in the dialog that pops up. You can add a keyword for faster access to the search engine optionally as well here.

Full-page translations speed up

Firefox supports privacy-friendly local translations for some time now. The translations do not require an Internet connection for translating content. The only time an Internet connection is required when Firefox downloads a language pack for the language that you want it to support.

Firefox 140 introduces a change for translated full-page content. Firefox used to translate the entire page by default immediately, when you selected the option. Now, Firefox will focus on the visible text, which, according to Mozilla, should speed up the translation process significantly.

Other changes and fixes

• You may now remove the Extension icon from the Firefox toolbar. Just right-click on the icon and select the "remove from toolbar" option to do so.  This moves the icon to the main Firefox menu, so that the listed extensions and functions remain accessible.
• Arabic builds of the Firefox web browser include an Arabic dictionary now by default which the Firefox spellchecker uses.
• Address auto-fill is now supported and enabled in Austria, Italy, and Poland.
• The Pocket toolbar icon and Pocket integrations on Firefox's New Tab Page have been removed. Mozilla announced the shutdown of Pocket earlier this year.
• Firefox will now escape less-than (<) and greater-than (>) symbols when serializing HTML attributes, making certain mXSS attacks on websites more difficult.

Developer changes

• The CSS Custom Highlight API is now supported.
• The UA styles for <h1> elements nested within sectioning elements have been removed.
• The SVG fetchpriority attribute is now supported for the SVG <feimage>, <image>, and <script> elements.
• The Cookie Store API is now supported.
• Support added for unspecified in cookies.SameSiteStatus. In addition, unspecified is now the default value for sameSite in cookies.set().
• Added platform support for aria-keyshortcuts in Linux, macOS, and Windows.
• Search in the Inspector panel is now improved.
• Added support for the pointerrawupdate event.
• Firefox now applies a uniform user agent (UA) style to <h1> elements, regardless of whether they are used inside <article>, <aside>, <nav>, or <section>.

Enterprise changes

• Firefox disables the option to load add-ons temporarily from now on if you prevent the installation of add-ons using policies. Previously, access to about:debugging was removed entirely.
• The DisableBuiltinPDFViewer policy no longer completely disables PDF.js; it changes the handler to send PDF files to the operating system.
• All Pocket related policies have been deprecated.

Security updates / fixes

Mozilla fixed 13 security related issues in Firefox 140.0. The severity rating is high, but Mozilla makes no mention of exploits in the wild. Still, it is recommended to upgrade Firefox asap to block potential attacks.

Firefox 140.0 download and update

Most non-managed versions of the Firefox web browser are updated automatically. The browsers check automatically for updates and will install new versions. These checks do not happen in real-time and some users may prefer to download and install the updates immediately.

This can be done in desktop versions of the Firefox web browser by selecting Menu > Help > About Firefox.

Manual downloads are also provided on Mozilla's official website.

Outlook

Firefox 141 will be released on July 22, 2025. The same is true for Firefox 140.1 and Firefox 128.13. Linux users can look forward to a big improvement in the release. Firefox will use less memory and no longer require a restart after an update has been applied by a package manager.

Additional information / resources

• Firefox 140 release notes
• Firefox 115.25.0 ESR release notes
• Firefox 128.12.0 ESR release notes
• Firefox 140.0 ESR release notes
• Firefox 140 for Developers
• Firefox 140 for Enterprise
• Firefox Security Advisories
• Firefox Release Schedule

Closing Words

Mozilla continues to add usability improvements to Firefox. Some add features that other browsers have supported for a long time, others, like Firefox's privacy-friendly translation feature, are quite unique and standout features.

Now You: have you tried the new Firefox release already? Let us know in the comment section below.