CentOS Errata and Security Advisory 2005:768
https://rhn.redhat.com/errata/RHSA-2005-768.html
The following updated files have been uploaded and are currently syncing to the mirrors:
x86_64: firefox-1.0.6-1.4.2.centos4.x86_64.rpm
src: firefox-1.0.6-1.4.2.centos4.src.rpm