spec-redirects redirect for "tor-fw-helper-spec" is broken/obsolete
https://spec.torproject.org/tor-fw-helper-spec redirects to https://gitweb.torproject.org/torspec.git/tree/tor-fw-helper-spec.txt, which says "Path not found".
The spec file was deleted (moved) in a872fc67b425470d0b0a09790dd6a376e4b0515a (2020-07-27).
Coincidentally I recently summarized the history of tor-fw-helper: tpo/anti-censorship/pluggable-transports/snowflake#40106 (comment 2784834)