A use after free flaw was found in Firefox's mObserverList object.
Malicious content could use this flaw to execute arbitrary code with
permissions of the user running Firefox.
This is now public:
This issue has been addressed in following products:
Red Hat Enterprise Linux 5
Red Hat Enterprise Linux 6
Red Hat Enterprise Linux 4
Via RHSA-2011:0471 https://rhn.redhat.com/errata/RHSA-2011-0471.html