Multiple vulnerabilities have been discovered in Mozilla Firefox and Mozilla Thunderbird, the most severe of which could allow for arbitrary code execution.

• Mozilla Firefox is a web browser used to access the Internet.
• Mozilla Firefox ESR is a version of the web browser intended to be deployed in large organizations.
• Mozilla Thunderbird is a free and open-source cross-platform email client, personal information manager, news client, RSS and chat client
  Successful exploitation of the most severe of these vulnerabilities could allow for arbitrary code execution in the context of the logged on user. Depending on the privileges associated with the user an attacker could then install programs; view, change, or delete data; or create new accounts with full user rights. Users whose accounts are configured to have fewer user rights on the system could be less impacted than those who operate with administrative user rights.

Read more... Cyber Security Advisories - MS-ISAC