A thunderbird security update has been released for CentOS 7.

CentOS-announce: CESA-2020:5235 Important CentOS 7 thunderbird Security Update

CentOS Errata and Security Advisory 2020:5235 Important

Upstream details at :   https://access.redhat.com/errata/RHSA-2020:5235

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

x86_64:
f57d7074e8e50a23c9a10a230c6edbd1f48bc3130046704525be72e10c371656 thunderbird-78.5.0-1.el7.centos.x86_64.rpm

Source:
6d147795bfe6c18c042e338932f14bdfcde9403bec0ccbb0c9c1132545645e57 thunderbird-78.5.0-1.el7.centos.src.rpm