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

Use FirefoxDriverService to explicitly define the driver path. Advanced Fixes

If you are running your C# Selenium tests in a CI/CD pipeline (such as Azure DevOps, GitHub Actions, or Docker containers), the lack of a display monitor or specific environment arguments will cause the driver service to fail immediately.

System.setProperty("webdriver.gecko.driver", "/usr/local/bin/geckodriver"); On Linux, install xvfb (X Virtual Framebuffer): GeckoDriver

Right-click your project in Visual Studio and select .

On Linux, install xvfb (X Virtual Framebuffer): using OpenQA

GeckoDriver and Firefox have a strict compatibility matrix. A very new Firefox version with an old GeckoDriver (or vice versa) will cause the service to fail.

from selenium import webdriver driver = webdriver.Firefox(executable_path=r'C:\WebDrivers\geckodriver.exe') or Docker containers)

Selenium cannot find the executable that launches Firefox.

using OpenQA.Selenium; using OpenQA.Selenium.Firefox;

public class FirefoxDriverFixture : IDisposable

Add a system environment variable NO_PROXY with the value localhost ⁠0.5.1 . 3. Kill Existing GeckoDriver Processes