Security researcher Mariusz Mlynski reported that when a page opens a new tab, a subsequent window can then be opened that can be navigated to about:newtab, a chrome privileged page. Once about:newtab is loaded, the special context can potentially be used to escalate privilege, allowing for arbitrary code execution on the local system in a maliciously crafted attack. Reference: http://www.mozilla.org/security/announce/2012/mfsa2012-60.html Acknowledgements: Red Hat would like to thank the Mozilla project for reporting this issue. Upstream acknowledges Security researcher Mariusz Mlynski as the original reporter of this flaw. Statement: Not Vulnerable. This issue does not affect the version of Firefox and Thunderbird as shipped with Red Hat Enterprise Linux 5 and 6.