Mozilla has officially released Firefox 140, along with corresponding updates to its long-term support branches - Firefox 115.25.0 and Firefox 128.12.0. The upcoming Firefox 141 branch has now entered the beta testing phase, with a planned release scheduled for July 22, 2025.
What's new in Firefox 140
Resizable pinned tabs
One of the notable user interface changes in Firefox 140 is the introduction of resizable pinned tabs within the vertical tabs panel. It allows adjusting the space allocated to pinned tabs using a simple drag-and-drop move.
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Unload Tab Option
The browser context menu now includes the "Unload Tab" option. It allows you to free up memory by unloading inactive tabs without closing them entirely.
Search Customization
A new option has been introduced for web developers and frequent searchers: the ability to add custom search engines directly from websites that define them via the <link rel="search"...> tag. Users can now do this via the context menu in search fields or via the Settings > Search interface.
Removable Extensions Toolbar Button
Firefox 140 further improves UI customization by allowing users to remove the extensions shortcut button from the toolbar. Extensions remain available in the main menu under the Extensions section.
On-demand translation of page
For improved accessibility and localization, the browser now supports on-demand translation of page content, where only visible sections are translated initially, with additional translations processed as the user scrolls.
Other
- Additionally, autofill support for web forms has expanded to include users in Poland, Italy, and Austria, following earlier availability in other major European countries.
- Removed legacy components related to the Pocket service, from the toolbar and New Tab page.
Technical and Web Development Advancements
Firefox 140 introduces several key technical improvements relevant to both end-users and developers:
- Linux sandboxing enhancements now restrict access to device drivers via
ioctl, improving system-level security. - Support has been added for the ARIA
aria-keyshortcutsattribute, enhancing keyboard navigation for users with disabilities. - The new CookieStore API enables asynchronous cookie management from web pages or service workers, offering greater flexibility for modern web applications.
- Custom Highlight API allows developers to apply dynamic, non-DOM-affecting styles to selected text regions, supporting advanced use cases like collaborative editing and syntax error highlighting.
- A new
pointerrawupdateevent provides higher-frequency pointer tracking, beneficial for applications requiring precise cursor movement detection. - In private browsing mode, sites can now use Service Workers to perform background tasks and access IndexedDB and Caching APIs with encrypted storage.
- The font size and style in <H1> elements have been unified , and are now independent of the use of <H1> within <article>, <aside>, <nav>, and <section> tags.
- Enhanced security measures now escape
<and>characters during HTML serialization, making certain types of XSS attacks more difficult to execute. - Web developers benefit from an improved DOM tree inspector featuring advanced search options, pseudo-class support, and sorting by element count.
- On mobile platforms, the Android version now includes a "Select All" function for bulk bookmark operations and strengthened security in private browsing mode.
Security Updates
Mozilla has addressed a total of 17 vulnerabilities in Firefox 140, six of which relate to critical memory management flaws such as buffer overflows and use-after-free errors, potentially exploitable for remote code execution.
A separate issue involved the built-in WebCompat extension, which allowed persistent identification of browser instances, including during private browsing sessions, due to exposure of a UUID via extension resources. This issue has been resolved in the latest update.
Download Firefox 140
To update to the latest version of Firefox on Windows, head to the browser’s menu and click on ‘About Firefox.’
If you prefer, you can also grab the installer directly from the following link: https://releases.mozilla.org/pub/firefox/releases/140.0/. From there, select the version that matches your operating system, language, and platform. The files are organized into subdirectories based on platform and interface language, and they include full offline installer packages for convenience.
For Linux users, the easiest way to get the latest version is by using your distribution’s package manager. For instance, if you’re on Ubuntu or Mint and have the official mozillateam PPA enabled, you can update Firefox by running the following command in a root terminal:
apt update && apt install firefox.
You can find the official release notes for this version here: https://www.mozilla.org/en-US/firefox/140.0/releasenotes/.
Beta Channel: Firefox 141
The Firefox 141 beta build focuses on memory optimization for Linux users and removes the requirement to restart the browser after package manager-based updates, improving usability for frequently updated environments.
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