Hi there
there is still a request to IP 52.28.43.223 in the code somewhere, which got blocked by Requestpolicy addon. After adding it to the ok list, client works fine under FF ESR. Just saying.
When you login you connect to our so-called metaserver, which handles everything related to accounts, lobby, tables, matchmaking, etc. When you actually start (or return to) a game the metaserver tells the client to connect to one of several gameservers. The IP you mention belongs to the gameserver in Frankfurt, so this looks like expected behavior.