I've experimented a little bit and found that synchronization only works in firefox when third-party cookies are enabled, otherwise buttons are greyed out. Adding everhelper.me as an exception didn't help either. Since I care about my privacy I don't like turning third-party cookies on. I'd be happy if you guys fixed that. Thank you and thank you for your service, it is well appreciated.
Servicio de atención al cliente por UserEcho