New way to sync preferences for Firefox add-on?

I maintain a Firefox add-on that stores some of the preference settings extensions.myextension.mypref

. To sync this preference across multiple Firefox profiles, I simply used the pref parameter services.sync.prefs.sync.extensions.myextension.mypref

to true. This worked fine for at least six months ago. But recently I noticed that this no longer works. While looking for a solution, I found that the article describing preference sync was moved to the "legacy content archive" on MDN.

Is this method for syncing custom Firefox add-ons no longer supported? And is there an alternative way?