I'm using Firefox for Android 68.1a1 (2019-08-04). I was able to find aboutsync in AMO and install it, but I get and error "the address isn't valid" when I visit about:sync in mobile. I tried restarting the application. I tried tapping into the addon via about:addons. (The only options there are 'Disable' and 'Uninstall'.)
Does that version of Firefox use the same Sync engine that desktop Firefox (version 68+) uses?