Geckodriver

geckodriver is the W3C WebDriver server for Firefox: a small Rust HTTP server that translates WebDriver JSON commands into Marionette / WebDriver BiDi messages handled inside the running Firefox. Lives in testing/geckodriver/.

Purpose

External tools (Selenium, Cypress, etc.) speak to geckodriver over HTTP; geckodriver then drives Firefox via the Marionette protocol implemented in testing/marionette/ and the WebDriver BiDi server in remote/webdriver-bidi/.

Directory layout

testing/geckodriver/
├── Cargo.toml
├── src/
│   ├── main.rs              # Entry point + arg parsing
│   ├── marionette.rs        # Marionette client transport
│   ├── browser.rs           # Firefox process management
│   ├── capabilities.rs      # WebDriver capabilities matching
│   ├── command.rs           # Command translation
│   ├── logging.rs           # Log levels and routing
│   └── ...
├── doc/                     # Project docs
├── webdriver/               # Shared types pulled from the webdriver crate
└── tests/

How it works

sequenceDiagram
    participant Test as Test (Selenium, etc.)
    participant GD as geckodriver
    participant FF as Firefox
    participant Mn as Marionette
    Test->>GD: HTTP POST /session {...}
    GD->>FF: spawn process
    GD->>Mn: TCP connect (Marionette port)
    Test->>GD: HTTP POST /session/{id}/url {url}
    GD->>Mn: WebDriver:Navigate {url}
    Mn-->>GD: ack
    GD-->>Test: 200 OK

Geckodriver is a workspace member in the top-level Cargo.toml.

Building and running

cd testing/geckodriver
cargo build --release
./target/release/geckodriver --version

In CI, geckodriver is built as part of the standard ./mach build along with the rest of the workspace crates and packaged separately.

Related

• Marionette + WebDriver BiDi
• DevTools server (CDP)