We'd love to add support for HTTP/2 to Fiddler, but at the moment we're blocked by a limit in the .NET Framework itself. Please consider adding your support to this issue: http://visualstudio.uservoice.com/forums/121579-visual-studio/suggestions/6264363-add-support-for-alpn-to-system-net-security-sslstr
Having said that, please keep in mind that Fiddler still works great on every HTTP2 site we've ever seen, as they all fall back to HTTP/1.1 where HTTP2 isn't supported.
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