Same-origin policy protections can be bypassed on pages with embedded iframes during page reloads, allowing the iframes to access content on the top level page, leading to information disclosure. This vulnerability affects Thunderbird < 52.3, Firefox ESR < 52.3, and Firefox < 55.
https://www.mozilla.org/security/advisories/mfsa2017-20/
https://www.mozilla.org/security/advisories/mfsa2017-19/
https://www.mozilla.org/security/advisories/mfsa2017-18/
https://www.debian.org/security/2017/dsa-3968
https://www.debian.org/security/2017/dsa-3928
https://security.gentoo.org/glsa/201803-14
https://bugzilla.mozilla.org/show_bug.cgi?id=1322896
https://access.redhat.com/errata/RHSA-2017:2534
https://access.redhat.com/errata/RHSA-2017:2456