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

This error is Selenium’s way of saying: “I tried to launch Firefox, but the bridge (GeckoDriver) connecting me to the browser collapsed before the connection could be established.”

For Java:

from selenium.webdriver.firefox.service import Service service = Service(executable_path='path/to/geckodriver', port=7055) # Classic Selenium port driver = webdriver.Firefox(service=service) This error is Selenium’s way of saying: “I

sudo apt-get install xvfb xvfb-run python your_selenium_script.py Or, use PyVirtualDisplay in Python:

The error occurs only in CI/CD (Jenkins, GitLab CI) but works on your local desktop. Cause 3: Port Conflict or Firewall Blocking The

Putting GeckoDriver in a folder that is not in your system's PATH environment variable and not specifying the path. If you just write new FirefoxDriver() without a Service object, Selenium will look in PATH and fail if it's not there. Cause 3: Port Conflict or Firewall Blocking The error mentions http://localhost . This is a real network address (127.0.0.1). If something else is using the port range GeckoDriver wants, or if your firewall/antivirus is blocking geckodriver.exe , the service cannot start. Diagnosing Port Conflicts By default, GeckoDriver picks a random free port between 10000 and 60000. If that specific port is locked by another application (like Docker, a local web server, or another WebDriver instance), the bind fails.

firefox --version If this fails, Firefox cannot be found in your PATH . Diagnosing Port Conflicts By default, GeckoDriver picks a

If you are reading this, you have likely been staring at a red, intimidating stack trace in your console. The error message, often truncated as cannot start the driver service on http://localhost when using Selenium with Firefox, is a classic automation roadblock.