A firefox security update has been released for CentOS 6.

CentOS Errata and Security Advisory 2020:0521 Important

Upstream details at :   https://access.redhat.com/errata/RHSA-2020:0521

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

i386:
d43d61853b40107c46c134fd55a9c534d542ac46eaf41fb552229f8f2847f611 firefox-68.5.0-2.el6.centos.i686.rpm

x86_64:
d43d61853b40107c46c134fd55a9c534d542ac46eaf41fb552229f8f2847f611 firefox-68.5.0-2.el6.centos.i686.rpm
c5c89229eb8001aae7c67813ab6decbad01f1490eed0ad6dacf6179d3f1ae909 firefox-68.5.0-2.el6.centos.x86_64.rpm

Source:
d76a824ccbbd2969af061d8b0e1fc79d69ad4ce24d4048d538b54d88aaa91f48 firefox-68.5.0-2.el6.centos.src.rpm