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

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 .

Ensure you aren't running an old version of GeckoDriver with a brand-new version of Firefox. The error is a common headache for C#

Ensure Firefox is updated to the latest stable release. 3. Configure Firewall Exceptions Loopback Issues: localhost isn't resolving to 127

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 driverService.Host = "127.0.0.1"

To prevent this error in the future, always wrap your driver initialization in a try-catch block and ensure you call driver.Quit() in a finally block or a using statement.