Mozilla has published a security advisory, highlighting vulnerabilities in Firefox & Firefox ESR on 1st June, 2021. It is recommended that you take the necessary precautions by ensuring your products are always updated.
For more information on these Mozilla updates you can follow these URLs:
https://www.mozilla.org/en-US/security/advisories/mfsa2021-23/
https://www.mozilla.org/en-US/security/advisories/mfsa2021-24/
The Guyana National CIRT recommends that users and administrators review these updates and apply them where necessary.
PDF Download: Mozilla Releases Security Updates for Firefox Firefox ESR.pdf
References
https://cyber.gc.ca/en/alerts/mozilla-security-advisory-37