A thunderbird security update has been released for CentOS 7.

CESA-2021:0661 Important CentOS 7 thunderbird Security Update

CentOS Errata and Security Advisory 2021:0661 Important

Upstream details at :   https://access.redhat.com/errata/RHSA-2021:0661

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

x86_64:
2079fcbe2c07aa0485612a667be1c81504654629f2931e7110664db306550787 thunderbird-78.8.0-1.el7.centos.x86_64.rpm

Source:
b1d0ae38d26dde16a81ac71b72f6368e625a7ccbed26d6dc8475c975d7569636 thunderbird-78.8.0-1.el7.centos.src.rpm