A firefox-esr security update has been released for Debian GNU/Linux 10 to address multiple security issues.

DSA 4956-1: firefox-esr security update

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Debian Security Advisory DSA-4956-1 security@debian.org
  https://www.debian.org/security/ Moritz Muehlenhoff
August 11, 2021   https://www.debian.org/security/faq
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Package : firefox-esr
CVE ID : CVE-2021-29980 CVE-2021-29984 CVE-2021-29985 CVE-2021-29986
CVE-2021-29988 CVE-2021-29989

Multiple security issues have been found in the Mozilla Firefox web
browser, which could potentially result in the execution of arbitrary
code.

For the stable distribution (buster), these problems have been fixed in
version 78.13.0esr-1~deb10u1.

We recommend that you upgrade your firefox-esr packages.

For the detailed security status of firefox-esr please refer to
its security tracker page at:
  https://security-tracker.debian.org/tracker/firefox-esr

Further information about Debian Security Advisories, how to apply
these updates to your system and frequently asked questions can be
found at:   https://www.debian.org/security/