Memory safety bugs were reported in Firefox 50.1 and Firefox ESR 45.6. Some of these bugs showed evidence of memory corruption and we presume that with enough effort that some of these could be exploited to run arbitrary code. This vulnerability affects Thunderbird < 45.7, Firefox ESR < 45.7, and Firefox < 51.
https://www.mozilla.org/security/advisories/mfsa2017-03/
https://www.mozilla.org/security/advisories/mfsa2017-02/
https://www.mozilla.org/security/advisories/mfsa2017-01/
https://www.debian.org/security/2017/dsa-3832
https://www.debian.org/security/2017/dsa-3771
https://security.gentoo.org/glsa/201702-22
https://security.gentoo.org/glsa/201702-13
http://www.securitytracker.com/id/1037693
http://www.securityfocus.com/bid/95762