WebExtension scripts can use the "data:" protocol to affect pages loaded by other web extensions using this protocol, leading to potential data disclosure or privilege escalation in affected extensions. This vulnerability affects Firefox ESR < 45.7 and Firefox < 51.
http://rhn.redhat.com/errata/RHSA-2017-0190.html
https://bugzilla.mozilla.org/show_bug.cgi?id=1319070
https://security.gentoo.org/glsa/201702-22
https://www.debian.org/security/2017/dsa-3771
https://www.mozilla.org/security/advisories/mfsa2017-01/