Microsoft has release updates to address a vulnerability in Firefox and Firefox ESR. It is recommended that you take the necessary precautions by ensuring your products are always updated.
Security vulnerabilities fixed in Firefox 67.0.3 and Firefox ESR 60.7.1
For more information on Microsoft May 2019 security updates you can follow this url:
The Guyana National CIRT recommends users and administration to review these updates and to apply them where necessary.
Microsoft release Security updates for Firefox and Firefox ESR (US-Cert)