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

DSA 4874-1: firefox-esr security update

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Debian Security Advisory DSA-4874-1 security@debian.org
  https://www.debian.org/security/ Moritz Muehlenhoff
March 24, 2021   https://www.debian.org/security/faq
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Package : firefox-esr
CVE ID : CVE-2021-23981 CVE-2021-23982 CVE-2021-23984 CVE-2021-23987

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

For the stable distribution (buster), these problems have been fixed in
version 78.9.0esr-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/