Cannot Start The Driver Service On Http Localhost Selenium Firefox C May 2026

If it works, add an exception for geckodriver.exe in your Windows Defender or Antivirus settings. 4. Clean Up Hanging Processes

Ensure Firefox is updated to the latest stable release. 3. Configure Firewall Exceptions

The error is a common headache for C# developers using Selenium with Firefox. It typically means the GeckoDriver executable is unable to establish a local network connection to start its internal server. 🛠️ Root Causes Port Conflicts: Another process is using the default port. Loopback Issues: localhost isn't resolving to 127.0.0.1 . If it works, add an exception for geckodriver

Your Selenium WebDriver, GeckoDriver, and Firefox versions are out of sync. 🚀 Top Solutions 1. Hardcode the Loopback Address

Security software is blocking the driver's execution. 🛠️ Root Causes Port Conflicts: Another process is

Right-click your project -> Manage NuGet Packages -> Update Selenium.WebDriver and Selenium.WebDriver.GeckoDriver .

Sometimes Selenium struggles to resolve the string "localhost." Forcing it to use the IPv4 loopback address often bypasses DNS or hostfile issues. driverService.Host = "127.0.0.1"

var driverService = FirefoxDriverService.CreateDefaultService(); driverService.Host = "127.0.0.1"; // Force IPv4 IWebDriver driver = new FirefoxDriver(driverService); Use code with caution. 2. Update Drivers and Browser

Since GeckoDriver starts a local web server to communicate with your code, firewalls might flag it as "unauthorized network activity." Temporarily disable your firewall to test.