CentOS Errata and Security Advisory 2009:0315
https://rhn.redhat.com/errata/RHSA-2009-0315.html
The following updated files have been uploaded and are currently syncing to the mirrors:
s390: updates/s390/RPMS/firefox-3.0.7-1.el4.centos.s390.rpm
s390x: updates/s390x/RPMS/firefox-3.0.7-1.el4.centos.s390x.rpm