A firefox security update has been released for CentOS 7.

CESA-2021:3791 Important CentOS 7 firefox Security Update

CentOS Errata and Security Advisory 2021:3791 Important

Upstream details at :   https://access.redhat.com/errata/RHSA-2021:3791

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

x86_64:
524031feb4b382103cd67a6e7a15219524577b7af9ecf3f8b7e5ca443bb043aa firefox-91.2.0-4.el7.centos.x86_64.rpm

Source:
4e7027af034a750ffc77063997838188070659cf83f92a9cdd9cd128c7076ce7 firefox-91.2.0-4.el7.centos.src.rpm