Debian follows the extended support releases (ESR) of Firefox. Support
for the 78.x series has ended, so starting with this update we're now
following the 91.x releases.
For Debian 9 stretch, these problems have been fixed in version
91.4.1esr-1~deb9u1.
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/source-package/firefox-esr
Further information about Debian LTS security advisories, how to apply
these updates to your system and frequently asked questions can be
found at: https://wiki.debian.org/LTS
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