firefox is vulnerable to sandbox restrictions bypass. Given a compromised sandboxed content process due to a separate vulnerability, it is possible to escape that sandbox by loading accounts.firefox.com
in that process and forcing a log-in to a malicious Firefox Sync account. Preference settings that disable the sandbox are then synchronized to the local machine and the compromised browser would restart without the sandbox if a crash is triggered.
access.redhat.com/errata/RHSA-2019:2694
access.redhat.com/security/updates/classification/#critical
bugzilla.mozilla.org/show_bug.cgi?id=1538008
bugzilla.mozilla.org/show_bug.cgi?id=1538015
www.mozilla.org/en-US/security/advisories/mfsa2019-27/
www.mozilla.org/security/advisories/mfsa2019-25/
www.mozilla.org/security/advisories/mfsa2019-26/
www.mozilla.org/security/advisories/mfsa2019-27/