A firefox security update has been released for CentOS 6.

CentOS Errata and Security Advisory 2020:0816 Important

Upstream details at :   https://access.redhat.com/errata/RHSA-2020:0816

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

i386:
d8d8733eeda0aa86cc16ac1dd750c0d5afdbcb52f5ce93605dd21553ffc21d03 firefox-68.6.0-1.el6.centos.i686.rpm

x86_64:
d8d8733eeda0aa86cc16ac1dd750c0d5afdbcb52f5ce93605dd21553ffc21d03 firefox-68.6.0-1.el6.centos.i686.rpm
d2e1d396de54e1471fecea64c22d5dd0341d4da55f66dc171acbdac71e9cd005 firefox-68.6.0-1.el6.centos.x86_64.rpm

Source:
7380f45e1c3c1cdfc90cff7d73979edba439b6cb1a38062f8efdffe85b435b56 firefox-68.6.0-1.el6.centos.src.rpm