20 20 78 78 78 ... Looks ASCII to me, Firefox on Windows. Could be OS.
OP is asking what are the line-drawing characters encoded as e.g: "┌" and "┐".
Since the charset returned by the app is UTF-8, these will be interpreted and encoded as UTF-8 and not whatever "ASCII - Extended" means.
1: https://gist.github.com/numpad0/7880ad1e3ed32b91d1ccf9c3374f...
Also confirmed with hexl-mode (hex editor in emacs)