Hi DavidNK, during the first several days when an update is available, the update server only reveals its existence to a fraction of the Firefox installations that check. The purpose of this is to build up a good test sample and determine whether there are any terrible show-stopping bugs in the new release before unleashing it on everyone.

If you really need Firefox 108.0 immediately, you can download a full installer and run it. It will detect that you want to do an update. The link for downloading the full installer is in this article: Custom installation of Firefox on Windows.

If you are concerned about data loss running a full installer, please consider making a backup of your profile folder which stores your personal data and settings: Back up and restore information in Firefox profiles.

I'm not sure if at the time you posted your question Firefox 108.0 already had been released as it would normally be possible to update manually via "Help -> About Firefox" unless updates have been suspended completely because there are known issues detected/reported.