A vulnerability exists during the installation of add-ons where the initial fetch ignored the origin attributes of the browsing context. This could leak cookies in private browsing mode or across different "containers" for people who use the Firefox Multi-Account Containers Web Extension. This vulnerability affects Firefox < 68.
https://www.mozilla.org/security/advisories/mfsa2019-21/
https://security.gentoo.org/glsa/201908-12
https://bugzilla.mozilla.org/show_bug.cgi?id=1528335
http://lists.opensuse.org/opensuse-security-announce/2019-10/msg00017.html
http://lists.opensuse.org/opensuse-security-announce/2019-10/msg00011.html
http://lists.opensuse.org/opensuse-security-announce/2019-10/msg00010.html
http://lists.opensuse.org/opensuse-security-announce/2019-10/msg00009.html