Firefox 129+ runs WebDriver BiDi-only by default (CDP off), so /json/version 404s and the socket is served directly at /session. Four fixes make the BiDi client actually work against it:
- probe(): fall back to a TCP check + ws://host:port/session when /json/version isn't advertised (don't open a probe WebSocket — that establishes session state and conflicts with session.new).
- websockets>=13 compat: ClientConnection dropped .closed; _ws_open() reads .state/.close_code across versions.
- session lifecycle: session.end on close() so a session never orphans (Firefox keeps one at a time, and an orphan blocks every later session.new); retry session.new once after ending.
- add create_context/close_context/get_url so automation runs in a fresh tab without disturbing the user's tabs.
zeekay
f336aaefc2