A thunderbird security update has been released for CentOS 7.

CESA-2021:0996 Important CentOS 7 thunderbird Security Update

CentOS Errata and Security Advisory 2021:0996 Important

Upstream details at :   https://access.redhat.com/errata/RHSA-2021:0996

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

x86_64:
412317b2522f388f60a8b9846d99020fa2c884e8557b0552ad09b4218e97803d thunderbird-78.9.0-3.el7.centos.x86_64.rpm

Source:
9b3ff2329273f188e644f9e8fb481e12ff32397fac7f7f9b4a689aa99d84529b thunderbird-78.9.0-3.el7.centos.src.rpm