[Fix] Firefox Sync Not Working for All Preferences (Options)

Firefox Sync is a very useful feature of Mozilla Firefox web browser. It allows users to sync their bookmarks (favorites), add-ons, preferences, login passwords, tabs, history, etc across their devices. So a Firefox user can customize the web browser according to his requirements such as changing options, installing extensions/themes, adding/removing bookmarks, signing into websites, etc in one device and then he can use the Sync feature to automatically synchronize all the customizations and settings across all other devices. It saves time and efforts and users can easily and quickly customize Firefox on all their devices.

In this article, we’ll talk about preferences sync in Mozilla Firefox web browser. The best and highly used part of Sync feature is preferences sync which automatically applies all custom settings across all Firefox installations in different devices. Users just need to customize Firefox options in one device and then they can take help of Sync feature to apply all customized settings in all other Firefox installations present in other devices.

To sync Options (about:preferences), Firefox creates a whitelist of options which will be synced automatically across devices. All options/preferences present in the whitelist are synced by Firefox.

This whitelist is stored in about:config page. You can launch about:config page in Firefox and search for services.sync.prefs.sync and you’ll find several preferences present on the page. These preferences are called Control Preferences. If a preference value is set to True, it means the preference is present in whitelist and will be synced by Firefox. If a preference value is set to False, it means the preference is not whitelisted and will not be synced by Firefox. You can manually enable/disable preferences to be synced by Firefox by changing their values to true or false.

Now sometimes Firefox users may face problems related to preferences sync. Some or all preferences may not sync properly across their devices. When they use Firefox Sync feature on other devices, they notice that Sync feature not working as expected and their custom preferences were not applied by the Sync feature.

It happens when a user created a new control preference to sync a custom preference. By default, Firefox will only sync those preferences that have a matching/existing control preference in all other devices. Firefox will not automatically copy or create custom control preferences to other devices where user is using Sync feature.

That’s why when a user use Sync feature in different devices, custom preferences are not synced by Firefox because the user needs to manually create all custom control preferences in other new devices.

Fortunately, to overcome this issue and to allow Firefox users to sync all preferences, Firefox provides a built-in preference/flag which can be used to force Firefox to sync all preferences.

If you are also facing problems with Firefox Sync feature and it’s not syncing your custom preferences properly, following steps will help you in fixing Firefox Sync functionality:

1. Open Mozilla Firefox and type about:config in the addressbar and press Enter. It’ll show you a warning message, click on “I accept the risk!” button. It’ll open Firefox’s hidden secret advanced configuration page i.e. about:config page.

2. Now type arbitrary in Search filter box and look for following preference in the window:

If the preference value is set to false, it means Firefox will not sync custom control preferences across devices.

3. To force Firefox to sync all preferences, double-click on services.sync.prefs.dangerously_allow_arbitrary preference and set it to true. Alternatively, you can right-click on the preference and select Toggle option.

That’s it. Now manually sync all things on your primary Firefox installation once so that Firefox can copy all your custom preferences and then you can use Sync on other devices to sync all preferences without any problem.

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