As per the recent post on the Mozilla Foundation Security Advisories page, dated September 7, 2021, Mozilla has released a new update for Firefox and Thunderbird that includes important new security fixes.
We advise you update Firefox and Thunderbird on all computer and devices, at home and at work, (campus and personal) before you use them to access webpages.
For information on how to update Firefox see the Mozilla Firefox page, Update Firefox to the latest release.