[Firefox] A note for Geckodriver

• Geckodriver
  • https://github.com/mozilla/gecko-dev/tree/master/testing/geckodriver
• WebDriver commands
  • https://github.com/mozilla/gecko-dev/blob/master/testing/webdriver/src/command.rs
• Geckodriver extension
  • https://github.com/mozilla/gecko-dev/blob/master/testing/geckodriver/src/command.rs

BTW, they are already fully in Rust. Wow.