Memory safety bugs were reported in Firefox 57 and Firefox ESR 52.5. 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 < 52.6, Firefox ESR < 52.6, and Firefox < 58.
https://www.mozilla.org/security/advisories/mfsa2018-04/
https://www.mozilla.org/security/advisories/mfsa2018-03/
https://www.mozilla.org/security/advisories/mfsa2018-02/
https://www.debian.org/security/2018/dsa-4102
https://www.debian.org/security/2018/dsa-4096
https://usn.ubuntu.com/3688-1/
https://usn.ubuntu.com/3544-1/
https://lists.debian.org/debian-lts-announce/2018/01/msg00036.html
https://lists.debian.org/debian-lts-announce/2018/01/msg00030.html
https://access.redhat.com/errata/RHSA-2018:0262
https://access.redhat.com/errata/RHSA-2018:0122