Cannot Start The Driver Service On Http Localhost Selenium Firefox C -

"Cannot start the driver service on http://localhost" in Selenium (Firefox/C#) typically means that the geckodriver

Task Manager

Check your for any background instances of geckodriver.exe or firefox.exe and end them. You can automate this via the command line as an administrator: taskkill /f /im geckodriver.exe taskkill /f /im firefox.exe 3. Handle Proxy and Loopback Settings "Cannot start the driver service on http://localhost" in

Sometimes headless causes issues. Test without headless first.

Windows: Run your IDE or command prompt as Administrator. Also, right-click geckodriver.exe → Properties → Unblock (if downloaded from internet).
macOS/Linux:
sudo chmod +x /path/to/geckodriver

test_firefox()