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.

不错的更新，AI翻译一下比较好。