I maintain a Firefox add-on which stores some settings in a preference extensions.myextension.mypref. In order to synchronize this preference between multiple Firefox profiles, I used to simply set the pref services.sync.prefs.sync.extensions.myextension.mypref to true. This used to work fine until at least half a year ago. But recently, I noticed that this does not seem to work any more. Searching for a solution I found that the article that describes syncing of preferences has been moved to the "archive of obsolete content" at MDN.
Is this method for syncing custom preferences of Firefox add-ons no longer supported? And is there any alternative way?