Mozilla Firefox is an open source Web browser. XULRunner provides the XUL Runtime environment for Mozilla Firefox. A memory corruption flaw was discovered in the way Firefox handles XML files containing an XSLT transform. A remote attacker could use this flaw to crash Firefox or, potentially, execute arbitrary code as the user running Firefox. A flaw was discovered in the way Firefox handles certain XUL garbage collection events. A remote attacker could use this flaw to crash Firefox or, potentially, execute arbitrary code as the user running Firefox. For technical details regarding these flaws, refer to the Mozilla security advisories. You can find a link to the Mozilla advisories in the References section of this errata. Firefox users should upgrade to these updated packages, which resolve these issues. For Red Hat Enterprise Linux 4, they contain backported patches to the firefox package. For Red Hat Enterprise Linux 5, they contain backported patches to the xulrunner packages. After installing the update, Firefox must be restarted for the changes to take effect.