A use-after-free vulnerability can occur while editing events in form elements on a page, resulting in a potentially exploitable crash. This vulnerability affects Firefox ESR < 52.6 and Thunderbird < 52.6.
https://www.debian.org/security/2018/dsa-4102
https://www.debian.org/security/2018/dsa-4096
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