Security software is blocking the driver's execution.
If it works, add an exception for geckodriver.exe in your Windows Defender or Antivirus settings. 4. Clean Up Hanging Processes
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 . Security software is blocking the driver's execution
Your Selenium WebDriver, GeckoDriver, and Firefox versions are out of sync. 🚀 Top Solutions 1. Hardcode the Loopback Address
Sometimes Selenium struggles to resolve the string "localhost." Forcing it to use the IPv4 loopback address often bypasses DNS or hostfile issues. Clean Up Hanging Processes The error is a
Ensure Firefox is updated to the latest stable release. 3. Configure Firewall Exceptions
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 Loopback Issues: localhost isn't resolving to 127
📍 Most "localhost" service errors are solved by explicitly setting the Host to 127.0.0.1 in the DriverService object. AI responses may include mistakes. Learn more
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.
Ensure you aren't running an old version of GeckoDriver with a brand-new version of Firefox.