A thunderbird Security Update has been released for CentOS 6

CentOS Errata and Security Advisory 2019:4205 Important

Upstream details at :   https://access.redhat.com/errata/RHSA-2019:4205

The following updated files have been uploaded and are currently
syncing to the mirrors: ( sha256sum Filename )

i386:
0cc0551f89a664502e3e8caf219aa589efbd8b567e0a5b6f503d2ffe56f43e26 thunderbird-68.3.0-3.el6.centos.i686.rpm

x86_64:
1a150c3f18980ecc2cd797f0a40a630f88ecfd0eaad1214d9b479317f934515f thunderbird-68.3.0-3.el6.centos.x86_64.rpm

Source:
b0e17df5d12434a926c2bc87d5bd141cb601b74bdb67591043af0179236395e8 thunderbird-68.3.0-3.el6.centos.src.rpm