Firefox 100: Update closes nine gaps

Firefox turns 100. With the new version, Mozilla fixes more than nine vulnerabilities. Security updates are also available for Firefox ESR and Thunderbird.

Mozilla has released Firefox 100.0 and Firefox ESR 91.9.0. As in the new Thunderbird 91.9.0, the developers have primarily eliminated security gaps and other bugs. We already presented some innovations to you yesterday. They concern subtitles in picture-in-picture video mode and language selection during installation.

The Firefox 100 update fixes at least nine security vulnerabilities, of which Mozilla classifies at least six as high risk. Another two vulnerabilities are classified as medium risk. Mozilla only lists vulnerabilities found internally in summary form, without specifying their number. According to Mozilla, some of these could potentially be exploited to inject and execute code. Attacks on Firefox vulnerabilities are currently not known.

More innovations

New in Firefox 100 is hardware-assisted video decoding for AV1 videos on Windows, which has been available on Linux since Firefox 98. The prerequisite is that supported graphics chips (GPU) are plugged into the computer. These are Intel GPUs from the 11th generation, AMD with RDNA2 architecture (except for Navi24), as well as Nvidia GeForce 30xx. Also requires the AV1 video extension from the Microsoft Store if not already installed.

Starting with this version, the Windows installer for Firefox is SHA-256 signed (SHA: Secure Hash Algorithm). For Windows 7, this means that update KB4474419 from 2019 must be installed. This provides support for SHA-2 and SHA-256.

▶The latest security updates

The update on

Firefox ESR

91.9.0 closes at least six vulnerabilities, at least five of which are considered high risk. These are essentially the same vulnerabilities fixed in Firefox 100. The new Tor Browser 11.0.11, based on Firefox ESR 91.9.0, is also already available. It brings the updated NoScript 11.4.5 extension.

The new Thunderbird version 91.9.0 primarily fixes those vulnerabilities that the mail program inherited from Firefox ESR. Firefox code is used for HTML processing, among other things. There are also some bug fixes


Mozilla plans to release Firefox 101 and Firefox ESR 91.10 on May 31st. Firefox 102 is to follow at the end of June, also as an ESR version. This begins a two-month transition phase in which Firefox ESR 91.x and 102.x will be maintained in parallel. This transition will end on August 23 with the release of Firefox ESR 91.13, the last release of this version branch.

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