A new update is available for Fedora Core - [SECURITY] Fedora Core 3 Update: firefox-1.0.6-1.2.fc3. Here the announcement:

Fedora Update Notification
FEDORA-2005-872
2005-09-10
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Product : Fedora Core 3
Name : firefox
Version : 1.0.6
Release : 1.2.fc3
Summary : Mozilla Firefox Web browser.
Description :
Mozilla Firefox is an open-source web browser, designed for standards
compliance, performance and portability.

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Update Information:

An updated firefox package that fixes as security bug is now
available for Fedora Core 3 and Fedora Core 4.

This update has been rated as having critical security
impact by the Fedora Security Response Team.

Mozilla Firefox is an open source Web browser.

A bug was found in the way Firefox processes certain
international domain names. An attacker could create a
specially crafted HTML file, which when viewed by the victim
would cause Firefox to crash or possibly execute arbitrary
code. The Common Vulnerabilities and Exposures project
(cve.mitre.org) has assigned the name CAN-2005-2871 to this
issue.

Users of Firefox are advised to upgrade to this updated
package that contains a backported patch and is not
vulnerable to this issue.

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* Fri Sep 9 2005 Christopher Aillon <caillon@redhat.com> 0:1.0.6-1.2.fc3
- Fix for CAN-2005-2871


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This update can be downloaded from:
http://download.fedora.redhat.com/pub/fedora/linux/core/updates/3/

6eaa113f4341531a82c3acdb38a8ce63 SRPMS/firefox-1.0.6-1.2.fc3.src.rpm
b3d5af88b33c7e160c897bc88f3d405e x86_64/firefox-1.0.6-1.2.fc3.x86_64.rpm
f2a098f972ca7f274d779c65bcc2bfe9 x86_64/debug/firefox-debuginfo-1.0.6-1.2.fc3.x86_64.rpm
597068a88783d1b0687cd4789a215267 i386/firefox-1.0.6-1.2.fc3.i386.rpm
820745933f8f81270e4981657432454b i386/debug/firefox-debuginfo-1.0.6-1.2.fc3.i386.rpm

This update can also be installed with the Update Agent; you can
launch the Update Agent with the 'up2date' command.