Multiple security issues have been found in the Mozilla Firefox web browser: Multiple memory safety errors, buffer overflows and other implementation errors may lead to the execution of arbitrary code or bypass of the same-origin policy. Also, a man-in-the-middle attack in the addon update mechanism has been fixed.
For the stable distribution (jessie), these problems have been fixed in version 45.5.0esr-1~deb8u1.
For the unstable distribution (sid), these problems have been fixed in version 45.5.0esr-1 and version 50.0-1 of the firefox source package.
We recommend that you upgrade your firefox-esr packages.