Wasm-pack test --safari --headless driver failed to bind port during startup

Build Environment Running Tests
1

Given this (abridged, macos wasm32 only) config.yml:

version: 2.1
executors:
  x86_64_macos:
    macos:
      # a version needs to be picked.  The latest, non-beta was chosen.
      xcode: "10.3.0"
    environment:
      CARGO_HOME: cargo
      HOMEBREW_NO_AUTO_UPDATE: 1
      HOMEBREW_NO_INSTALL_CLEANUP: 1
      LLVM_SYS_70_PREFIX: /usr/local/opt/llvm
jobs:
  wasm32_safari_examples_spawn_chain_test:
    executor: x86_64_macos
    steps:
      - run:
          name: Enable safari driver
          command: sudo /usr/bin/safaridriver --enable
      - run:
          name: Install LLVM
          command: brew install llvm
      - checkout
      - restore_cache:
          keys:
            - v4-cargo-cache-{{ arch }}-{{ checksum "Cargo.lock" }}-wasm32-safari
      - run:
          name: Install rustup and nightly toolchain
          command: |
            curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y --default-toolchain=nightly
            echo 'export PATH=/Users/distiller/project/cargo/bin:$PATH' >> $BASH_ENV
      - run:
          name: Install wasm32 target
          command: rustup target add wasm32-unknown-unknown --toolchain nightly
      - run:
          name: Install wasm-bindgen-cli
          command: cargo +nightly install wasm-bindgen-cli
      - run:
          name: Install wasm-pack
          command: curl https://rustwasm.github.io/wasm-pack/installer/init.sh -sSf | sh
      - run:
          name: Run all tests
          working_directory: "examples/spawn-chain"
          command: wasm-pack test --safari --headless
      - save_cache:
          key: v4-cargo-cache-{{ arch }}-{{ checksum "Cargo.lock" }}-wasm32-safari
          paths:
            - cargo
            - target/debug/.fingerprint
            - target/debug/build
            - target/debug/deps
workflows:
  version: 2
  primary:
    jobs:
      - wasm32_safari_examples_spawn_chain_test

I can’t get safaridriver to work:

Running headless tests in Safari with `/usr/bin/safaridriver`
Spawning Geckodriver...                           
driver status: exit code: 1
error: driver failed to bind port during startup
error: test failed, to rerun pass '--test web'
Error: Running Wasm tests with wasm-bindgen-test failed
Caused by: failed to execute `cargo test`: exited with exit code: 1
Exited with code 1

I already have sudo /usr/bin/safaridriver --enable, so I’m not sure what is missing. Has anyone had this driver failed to bind port during startup error before?

Support: this is in https://circleci.com/gh/lumen/lumen/3489 if you need the full build output.