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Firefox Sync gives you the ability to sync your preferences across all your Firefox Desktop devices. Learn more.

[[Template:aboutconfigwarning]] Firefox Sync gives you the ability to sync your preferences across all your Firefox Desktop devices. Please note that preference syncing is only supported via Firefox Desktop. We’ve chosen the list of preferences that can be synced so that the average user can sync preferences directly from the Firefox Desktop UI. However, advanced users, who want more control over which '''about:config''' preferences are synced, will benefit the most from this article. 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'' via '''about:config'''. For example, the '''browser.urlbar.suggest.history''' preference will be synced only if the boolean '''services.sync.prefs.sync.browser.urlbar.suggest.history''' control preference has been set to ''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 the '''services.sync.prefs.sync.''some_preference''''' preference to ''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, '''services.sync.prefs.dangerously_allow_arbitrary''', which controls this behavior. If you set this preference to ''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 '''services.sync.prefs.dangerously_allow_arbitrary''' preference to ''true'', perform the sync once, and then set this preference back to ''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 '''services.sync.prefs.dangerously_allow_arbitrary''' was set to ''true''.{/note}