* It is possible to configure Firefox such that whether a Referer is sent can depend on whether the two sites are in the same registered domain.
* Providers are distinguished from each other in the Social API via registered domain.
===Internet Explorer===
Integrate [http://blogs.msdn.com/b/ieinternals/archive/2009/09/19/private-domain-names-and-public-suffixes-in-internet-explorer.aspx http://blogs.msdn.com/b/ieinternals/archive/2009/09/19/private-domain-names-and-public-suffixes-in-internet-explorer.aspx] somehow.
==Standards==