I assume that you are Sync'ing Preferences for this answer. Specifically, which settings are getting changed by Sync? For many settings in '''about:config''' there is a corresponding "sync" setting to disable the particular setting from being synchronized with all the other Preferences. '''services.sync.prefs.sync.''' would be the start of the "corresponding" prefs You can use that string in the "Search" field at the top of '''about:config''' ''[typed in the URL bar and hit enter]'' to filter only prefs that start with that string, to see all the prefs that I am referring to.