CVE-2016-5284

Mozilla Firefox before 49.0 and Firefox ESR 45.x before 45.4 rely on unintended expiration dates for Preloaded Public Key Pinning, which allows man-in-the-middle attackers to spoof add-on updates by leveraging possession of an X.509 server certificate for addons.mozilla.org signed by an arbitrary built-in Certification Authority.

Source: CVE-2016-5284