docs: private static Executable locateFirefoxBinaryFromSystemProperty() {
      String binaryName = System.getProperty(FirefoxDriver.SystemProperty.BROWSER_BINARY);
      if (binaryName == null)
        return null;
  
      File binary = new File(binaryName);
      if (binary.exists() && !binary.isDirectory())
        return new Executable(binary);
  
      Platform current = Platform.getCurrent();
      if (current.is(WINDOWS)) {
        if (!binaryName.endsWith(".exe")) {
          binaryName += ".exe";
        }
  
      } else if (current.is(MAC)) {
        if (!binaryName.endsWith(".app")) {
          binaryName += ".app";
        }
        binaryName += "/Contents/MacOS/firefox-bin";
      }
  
      binary = new File(binaryName);
      if (binary.exists())
        return new Executable(binary);
  
      throw new WebDriverException(
        String.format("'%s' property set, but unable to locate the requested binary: %s",
                      FirefoxDriver.SystemProperty.BROWSER_BINARY, binaryName));
    }