When the Mozilla Updater is run, if the Updater's log file in the working directory points to a hardlink, data can be appended to an arbitrary local file. This vulnerability requires local system access. Note: this issue only affects Windows operating systems. This vulnerability affects Firefox ESR < 45.5 and Firefox < 50.
https://www.mozilla.org/security/advisories/mfsa2016-90/
https://www.mozilla.org/security/advisories/mfsa2016-89/
https://security.gentoo.org/glsa/201701-15
https://bugzilla.mozilla.org/show_bug.cgi?id=1246945