from selenium.webdriver.firefox.options import Options options = Options() options.binary_location = r'C:\Program Files\Mozilla Firefox\firefox.exe' # Windows driver = webdriver.Firefox(options=options) Cause 5: The Headless/Background Mode Trap When running Selenium on a headless server (Linux without a GUI, or Docker container), GeckoDriver attempts to create a graphical display. If it fails, the entire service crashes with the localhost error.
import io.github.bonigarcia.wdm.WebDriverManager; WebDriverManager.firefoxdriver().setup(); // Auto-downloads and sets path WebDriver driver = new FirefoxDriver(); from selenium
On Linux, install xvfb (X Virtual Framebuffer): This article will dissect every possible cause of
Do not worry. This article will dissect every possible cause of this error—from version hell and path misconfigurations to operating system permissions and port conflicts. By the end, your Firefox automation will start cleanly, every time. Before fixing the problem, you must understand the players involved. Selenium does not control Firefox directly. It uses a separate executable called GeckoDriver . The communication flow looks like this: Selenium does not control Firefox directly
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.