Security researcher Tyson Smith reported a use-after-free during the shutdown process. This was caused by a race condition when media decoder threads are created during the shutdown process in some circumstances. This leads to a potentially exploitable crash when triggered. External Reference: http://www.mozilla.org/security/announce/2015/mfsa2015-53.html Acknowledgements: Red Hat would like to thank the Mozilla project for reporting this issue. Upstream acknowledges Tyson Smith as the original reporter. Statement: This issue does not affect the version of firefox and thunderbird as shipped with Red Hat Enterprise Linux 5, 6 and 7.