> Does this mean that TBB too - as from September 2017 - will no longer be available for the XP series?
Yes. XP is now a 17 years old OS riddled with security vulnerabilities, you can't expect developers to support it for a longer time. See https://trac.torproject.org/projects/tor/ticket/21080 "My guess is we're going to triage and decide not to try to rescue XP when Mozilla has decided to abandon it."
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