in the current state the firefox update will be only triggered in the user context of the first user who started firefox on a multisession host. Unfortunately, if you work on a multisession environment with multiple hosts the update will not be installed until the user logs in again to this specific host. The reason for this behaviour is that the scheduled task is created in the user context and runs only if the user is logged in.
It would be great to have a more stable and reliable way to automatically update firefox. Like MS Edge or Chrome.