Supported at least since IE 8 (2009) [1], not sure how multiple instances behaved before. [1] https://blogs.msdn.microsoft.com/ie/2009/05/06/session-cookies-se

Supported at least since IE 8 (2009) [1], not sure how multiple instances behaved before. [1] https://blogs.msdn.microsoft.com/ie/2009/05/06/session-cookies-sessionstorage-and-ie8-or-how-can-i-log-into-two-webmail-accounts-at-the-same-time/ https://blogs.msdn.microsoft.com/ie/2009/05/06/session-cooki...