using System; using OpenQA.Selenium; using OpenQA.Selenium.Firefox; using WebDriverManager; using WebDriverManager.DriverConfigs.Impl; namespace SeleniumFirefoxSetup class Program static void Main(string[] sender) IWebDriver driver = null; try // 1. Resolve driver versioning automatically new DriverManager().SetUpDriver(new FirefoxConfig()); // 2. Configure the driver service to avoid localhost resolution bugs FirefoxDriverService service = FirefoxDriverService.CreateDefaultService(); service.Host = "127.0.0.1"; // 3. Define browser options FirefoxOptions options = new FirefoxOptions(); // options.AddArgument("--headless"); // Uncomment if running on a CI/CD server // 4. Initialize driver driver = new FirefoxDriver(service, options); // Execute Test driver.Navigate().GoToUrl("https://example.com"); Console.WriteLine("Title: " + driver.Title); catch (WebDriverException ex) Console.WriteLine($"Selenium Initialization Error: ex.Message"); finally // 5. Always quit the driver to release the ports and kill binaries if (driver != null) driver.Quit(); driver.Dispose(); Use code with caution.
When executing tests on a headless Linux server, you must pass the --headless argument to Firefox via C#:
The WebDriverManager checks your installed Firefox version, finds the matching geckodriver.exe , downloads it to a temporary cache, and points Selenium to it automatically. This eliminates the "Cannot start driver service" error caused by missing files or path issues 99% of the time.
If multiple microservices face this issue, add a machine-wide bypass rule: Press Win + R , type sysdm.cpl , and hit . using System; using OpenQA
service = Service(executable_path='path/to/geckodriver') driver = webdriver.Firefox(service=service)
using System.Diagnostics; foreach (var process in Process.GetProcessesByName("geckodriver")) process.Kill(); Use code with caution. 3. Manage Port Conflicts and Firewall Blocks
If it works, add an exception for geckodriver.exe in your Windows Defender or Antivirus settings. 4. Clean Up Hanging Processes When executing tests on a headless Linux server,
Occasionally, restrictive group policies or endpoint protection (like CrowdStrike or Windows Defender) will block the driver from creating a subprocess. Whitelisting the folder where geckodriver.exe resides often resolves this. 5. Headless Mode and Environment Variables
This error often appears when running tests in parallel or on resource-limited machines.
Increase the command timeout when initializing the FirefoxDriver: [TearDown] public void TearDown()
You can force the FirefoxDriverService to use the explicit IPv4 loopback address in your C# code:
driver.Navigate().GoToUrl("https://example.com"); Console.WriteLine(driver.Title);
[TearDown] public void TearDown()