A firefox security update has been been released for CentOS 7.

CentOS-announce: CESA-2020:5099 Critical CentOS 7 firefox Security Update

CentOS Errata and Security Advisory 2020:5099 Critical

Upstream details at :   https://access.redhat.com/errata/RHSA-2020:5099

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

x86_64:
54c6e6aa53fe175c25dc35fe3f6476d9b195d85a4fc5e64d5625d1731cc5b1ce firefox-78.4.1-1.el7.centos.i686.rpm
d8f95fca6716286e91c7ab7b9be9bd359800c870cc0bdb90128bf93397e9352d firefox-78.4.1-1.el7.centos.x86_64.rpm

Source:
48cf4a93202542b3895382c41bdb9659a38b32186aca558fd35b15d62ddafafe firefox-78.4.1-1.el7.centos.src.rpm