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Firefox Sync allows you to sync your preference settings across all your Firefox Desktop devices. Learn more.

[[Template:aboutconfigwarning]] Firefox Sync allows you to [[How do I choose what types of information to sync on Firefox?|choose the types of data to sync]] across devices. Please note that syncing Firefox preference settings is only supported in Firefox Desktop. We’ve chosen the list of preferences that can be synced so that the average user can sync those settings directly from the Firefox Desktop user interface (UI). Advanced users who want more control over which preferences are synced, however, will benefit the most from this article. __TOC__ =Preferences that Firefox will sync= Firefox whitelists the preferences that it will sync. Every preference that is synced appears in this whitelist. The whitelist itself is also stored in preferences, which includes every preference starting with '''services.sync.prefs.sync.''' (also known as a “control preference”). These preferences will only be synced if their control preferences have been set to ''true'' in the [[Configuration Editor for Firefox]] ('''about:config''' page). For example, the {pref browser.urlbar.suggest.history} preference will be synced only if the {pref services.sync.prefs.sync.browser.urlbar.suggest.history} control preference has been set to {pref true}. =Disable sync for a default preference= Firefox automatically creates a default whitelist, which is how it determines the default list of preferences to sync. If you don’t want to sync a default preference, you can change its control preference to ''false''. For example, if you set {pref services.sync.prefs.sync.<''some preference''>} to {pref false}, then its related preference won’t be synced. =Sync custom preferences= For safety reasons, only preferences that already have a local control preference will be applied locally. For example, if you want to sync a new preference that isn’t in the default list, you will need to ensure the new control preference has been created on every device. Firefox Sync won’t automatically copy custom control preferences to new devices. This can be an issue for users who have many custom preferences synced. When adding a new device, they will need to ensure all the custom control preferences are set up on the new device before those preferences are synced. To assist setting up new devices, there’s another preference, {pref services.sync.prefs.dangerously_allow_arbitrary}, which controls this behavior. If you set this preference to {pref true}, then all preferences will be synced to the new device and not just those with an existing control preference. Therefore, users with many custom preferences can set the {pref services.sync.prefs.dangerously_allow_arbitrary} preference to {pref true}, perform the sync once, and then set this preference back to {pref false}. This will cause all remote preferences to be applied. {note}This behavior changed in Firefox version 68. Prior to version 68, Firefox always acted as if the preference {pref services.sync.prefs.dangerously_allow_arbitrary} was set to {pref true}.{/note}