Hey there! It's great that you're trying to sync your preferences between your Windows and Ubuntu installations. Sometimes, even after setting "services.sync.prefs.dangerously_allow_arbitrary" to True, some preferences might not sync as expected. Here's what you can do: First, double-check that the preference name is correct and that there are no typos. Also, make sure you've restarted both browsers after making the change. If the issue persists, it's worth trying a couple of things: 1. On both devices, set "services.sync.prefs.sync.browser.compactmode.show" to True as well. 2. Wait for a bit, as sometimes syncing might take a little time. If none of this works, it might be helpful to bring this up in our community forum, where you can get more personalized assistance from our fellow Firefox enthusiasts.

WARNING from the moderator team: Changing Firefox preferences from the about:config page can sometimes break Firefox or cause strange behavior. You should only do this if you know what you're doing. Please read Firefox Advanced Customization and Configuration Options to learn more.

Some background for this discussion:

By default, Firefox will only upload preferences to the Sync cloud if instructed to do so. Take your theme for example. You'll find this pair of preferences:

• extensions.activeThemeID
• services.sync.prefs.sync.extensions.activeThemeID

If the second of those preferences is set to true, then Firefox will push/upload that value up to the Sync cloud and will update the first preference if it gets a new value back from the Sync cloud.

But what about a preference that doesn't have that corresponding services.sync.prefs.sync. instruction? For example:

• browser.compactmode.show

Firefox will neither push/upload that value up to the Sync cloud nor update the preference if it happens to get a new value back from the Sync cloud.

What does "dangerously_allow_arbitrary" do?

This preference modifies the last part of process. Even if browser.compactmode.show doesn't have a corresponding Sync process, Firefox **will** accept the new value it receives from the Sync cloud.

What it does NOT do is replace the push/upload behavior. You still need to create a services.sync.prefs.sync. preference to accomplish that. You can set it on the one you tend to tweak, or on all of your Firefoxes. Here's how:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button accepting the risk.

More info on about:config: Configuration Editor for Firefox. The moderators would like us to remind you that changes made through this back door aren't fully supported and aren't guaranteed to continue working in the future.

(2) In the search box in the page, type or paste services.sync.prefs.sync.browser.compactmode.show and pause while the list is filtered

Firefox should show a bar with Boolean Number String and a "+" button.

(3) Keep the selection on Boolean and click the "+" button to add a new preference. If the preference value is not set to true automatically, double-click it (or click the Toggle button or Reset button at the right end of the row) to set the value to true

@jscher2000 thanks for the explanation!

Is there a way to push/upload all the preferences, without creating a ``sync`` preference for each one individually?

Is there a way to push/upload all the preferences, without creating a ``sync`` preference for each one individually?

I'm not aware of one. It would cause a tremendous amount of clutter...

I personally wouldn't mind the clutter if it made syncing easier. But I can accept that there isn't such an option. Thanks again for the explanation, I've marked your answer as the solution