hi, are you using websense security products in your environment? if yes no update will be offered to systems where this third-party software is present at the moment because it causes firefox versions 48 and above to crash immediately on startup. if websense isn't a factor for you, then you could try if installing the hotfix addon from https://addons.mozilla.org/firefox/addon/firefox-hotfix/ helps - it determines the websense status of a system and enables updates if it isn't detected. this addon is normally getting installed automatically in the background, which might not happen for users who haven't set automatic updates to on though...

I don't know what websense is, never heard of it, so i'm very sure we don't use it at work. Makes it strange that firefox believe we have it. It's not ideal to go around install patches manually on all machines, so most likely firefox detect this thing wrong. I have not changed anything about automatic update, all installs are defeault.