Except where noted, everything here applies to both Firefox 90 and the Firefox 78.12 ESR.
- On Windows, Firefox now supports background updates. This does not apply to the ESR.
- On Windows, the version number was removed from DisplayName in the Uninstall data for Firefox in the registry. See bug 1713393 for more details.
- It was possible to remove a locked extension. This was fixed in bug 1658768.
- When setting the OfferToSaveLogins policy to false, some items in preferences were still clickable. This was fixed in bug 1692159. This was not a problem in the ESR.
- If the DisableAppUpdate policy was set to true, typing "update firefox" in the URL bar still offered to update Firefox. This was fixed in bug 1710796.
- The AutoLaunchProtocolsFromOrigins policy has been added. This allows you to define a list of external protocols that can be used from listed origins without prompting the user. It is based on the Chrome policy of the same name.
- The BackgroundAppUpdate policy has been added. This allows you to control background updates. This does not apply to the ESR.
- 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.