WebExtensions could use popups and panels in the extension UI to load an "about:" privileged URL, violating security checks that disallow this behavior. This vulnerability affects Firefox < 56.Referenceshttp://www.securitytracker.com/id/1039465https://www.mozilla.org/security/advisories/mfsa2017-21/https://bugzilla.mozilla.org/show_bug.cgi?id=1380597http://www.securityfocus.com/bid/101057
