What I didn't know, however, apart from this appalling demonstration to me today that they somehow know about my non-F/book Yahoo accounts
Probably just by reading your cookie file. I bet tacit or any admin here could do the same (if they wanted to).
when you browse for people - relatives in my case - they offer you complete strangers to "friend" who are on your relative's lists. Complete strangers. Never heard of them.
"Friends of friends" -- in some cases total strangers, in some cases ex-lovers.
What's the big whoop?
