Mozilla developer Kris Maglione reported a mechanism where WebExtension APIs could be used to escalate privilege. This could allow arbitrary web content to execute code with the privileges of a particular WebExtension when using these API calls. Depending on the privileges of the extension used, this could result in personal information theft and cross-site scripting (XSS) attacks, including theft of browser cookies. This is mitigated by the requirement to have a WebExtension installed that is vulnerable to this issue. External Reference: https://www.mozilla.org/security/announce/2015/mfsa2015-148.html Acknowledgements: Red Hat would like to thank the Mozilla project for reporting this issue. Upstream acknowledges Kris Maglione 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.