CentOS Errata and Security Advisory 2007:0981
https://rhn.redhat.com/errata/RHSA-2007-0981.html
The following updated files have been uploaded and are currently syncing to the mirrors:
i386: thunderbird-1.5.0.12-0.5.el4.centos.i386.rpm
src: thunderbird-1.5.0.12-0.5.el4.centos.src.rpm