The maintenance service in Mozilla Firefox before 47.0 and Firefox ESR 45.x before 45.2 on Windows does not prevent MAR extracted-file modification during updater execution, which might allow local users to gain privileges via a Trojan horse file.
https://bugzilla.mozilla.org/show_bug.cgi?id=1237219
http://www.securitytracker.com/id/1036057
http://www.securityfocus.com/bid/91075
http://www.mozilla.org/security/announce/2016/mfsa2016-55.html