It sounds like you’re running into the error:
Cannot start the driver service on http://localhost
with Selenium and Firefox.
This usually means the geckodriver (Selenium’s bridge to Firefox) failed to start or communicate properly. It sounds like you’re running into the error:
If you are automating web tests with Selenium in C#, few things are as frustrating as setting up your environment, writing your first script, hitting "Run," and being greeted by a critical red exception:
OpenQA.Selenium.DriverServiceNotFoundException: Cannot start the driver service on http://localhost:XXXXX/ Cannot start the driver service on http://localhost with
Or perhaps you are seeing:
OpenQA.Selenium.WebDriverException: Cannot start the driver service on http://localhost:4444/ This usually means the geckodriver (Selenium’s bridge to
This error is the bane of many Selenium developers, particularly those working with the Firefox browser in a C# .NET environment. It essentially means your C# code tried to knock on the door of the GeckoDriver application, but nobody answered.
In this deep dive, we will explore exactly why this happens and, more importantly, how to fix it. We will cover the common pitfalls, the Path variable issues, and the modern solution using NuGet packages.
driver = webdriver.Firefox(service=service)
using OpenQA.Selenium;
using OpenQA.Selenium.Firefox;
using System;
class Program
static void Main()
var driverPath = @"C:\drivers\geckodriver"; // full folder path containing geckodriver.exe
var service = FirefoxDriverService.CreateDefaultService(driverPath);
service.HideCommandPromptWindow = true;
service.Port = 0; // let system pick an open port
var options = new FirefoxOptions();
options.AddArgument("--headless"); // optional for CI
using (var driver = new FirefoxDriver(service, options, TimeSpan.FromSeconds(60)))
driver.Navigate().GoToUrl("https://example.com");
Console.WriteLine(driver.Title);
