Except where noted, everything here applies to only to Firefox 91. Firefox 91 is the next ESR, so going forward, only bug fixes will be backported to the Firefox 78 ESR.
- Firefox now supports logging into Microsoft, work, and school accounts using Windows single sign-on. More information is available here.
- Enterprise policies are now supported for Snap users on Linux. This was fixed in bug 1717216. This was fixed in the Firefox 78 ESR as well.
- The WindowsSSO policy has been added. This allows you to enable or disable the new Windows SSO feature.
- The SearchEngines policy has been updated to support setting the query charset (Encoding). It now defaults to UTF-8. Previously it defaulted to windows-1252.
- The Firefox 78 ESR is the last version of Firefox that supports Flash. The last version of that ESR will be 78.15 which is scheduled to be released on 2021-10-05. This means that Flash will officially be out of support on Firefox when the Firefox 78 ESR reaches EOL on 2021-11-02.
- The Firefox 78 ESR is the last version of Firefox that supports macOS versions < 10.12.