Prior to May 22nd, I used my Firefox account to SYNC my bookmarks, add-ons and preferences between my Tor Browser and Firefox browser applications. This appears to be a result of Tor Browser's upgrade from version 8.0.5 to 8.5 on that same date. While I am successfully logged into my Firefox account, no 'auto' sync has happened since May 22nd and attempts to manually sync yield no feedback.
How can I restore this functionality? It is not obvious to me that there are settings in about:config that would potentially address this regression issue.