This setting has always worked for me. What is does it update a file in a folder whose name starts with Mozilla and is stored in the hidden folder C:\ProgramData\ On my system, it's C:\ProgramData\Mozilla-''random-GUID?''\updates\308046B0AF4A39CB In that folder, my update-config.json file has this text (I bolded the really critical part which records my update preference): {"__DEFAULTS__":{"app.update.auto":true,"app.update.background.enabled":true},'''"app.update.auto":false'''} So this leads to two thoughts: (1) Maybe there is a problem with your update-config.json file -- not being created, getting erased, etc. (2) Maybe there is some other software on your computer that force-installs program updates. We have that on our office computers, but it's not typical on a home computer.