Several security issues have been found in the Mozilla Firefox web browser: Multiple memory safety errors and other implementation errors may lead to the execution of arbitrary code, denial of service, cross-site request forgery or information disclosure.
For the stable distribution (stretch), these problems have been fixed in version 52.9.0esr-1~deb9u1.
We recommend that you upgrade your firefox-esr packages.
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/