Firefox 140 improves web translation performance and pinned tabs

The latest Firefox update brings the browser up to version 140 with various new features and improvements. For example, the internal translation feature is more resource-efficient and pinned tabs are more flexible. The developers have also fixed several security vulnerabilities. Firefox ESR and Tor Browser also received security updates.

Mozilla plans to release versions Firefox 141 and Firefox ESR 140.1, ESR 128.13, and ESR 115.26 on July 22nd, 2025.

What’s new in Firefox 140?

Firefox’s local translation feature initially only translates content that’s currently visible in the browser window. Only when you scroll to previously unseen sections of a page will it then translate that content. This reduces resource consumption and improves performance.

If you use the vertical tabs introduced with Firefox 136 in combination with pinned tabs, you can now keep more (or fewer) pinned tabs in view. All you have to do is move the separator line.

Firefox now also supports even more search engines that you can add. To do this, right-click in the search field of a (supported) website and select “Add search engine” from the context menu. For Firefox users in the US on version 139 and higher, Mozilla added the AI-based search engine Perplexity to the standard selection in mid-June at the request of users.

Security updates in Firefox 140

Mozilla’s 2025-51 Security Advisory shows 17 vulnerabilities fixed for Firefox 140. Mozilla categorizes one of the externally reported vulnerabilities as high risk. It’s a use-after-free vulnerability (CVE-2025-6424) in the FontFaceSet API. An attacker could exploit it by provoking a crash that would execute injected code.

Five internally discovered vulnerabilities, summarized under CVE-2025-6436, are also considered high risk. All other vulnerabilities that Mozilla’s developers have fixed in Firefox 140 are categorized as medium or low risk. One of them, CVE-2025-6431, only affects Firefox for Android.

Updates for Firefox ESR and Tor Browser

Firefox 140 is the newest standard version for Firefox ESR. Firefox ESR 140 will initially be identical to the regular Firefox 140, but it will only receive security updates and important bug fixes, not new features.

Mozilla will support Firefox ESR 128 and ESR 140 in parallel until August 19th, when this transition phase will end. Firefox ESR 115 is also planned to end support with the August update, unless Mozilla decides to extend the deadline again (to be announced in August).

Mozilla has updated its long-term versions Firefox ESR 128 and ESR 115 and also fixed some vulnerabilities, namely the FontFaceSet flaw mentioned above. Five vulnerabilities have been fixed in Firefox ESR 128.12.0 and two in Firefox ESR 115.25.0.

The updated Tor Browser 14.5.4 is based on Firefox ESR 128.12.0 and comes with the new NoScript version 13.0.8. The Tor developers state that they have also ported security fixes from Firefox 140. An update for Tor Browser 13.5 to version 13.5.19 is also available if you are using Windows 7 / 8.1 or macOS 10.12 to 10.14. Tor Browser 13.5.19 is based on Firefox ESR 115.25.0 and also includes NoScript 13.0.8.