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

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

In CI/CD environments, implement a retry mechanism that waits a few seconds and retries driver initialization if the first attempt fails.

service = Service(executable_path='geckodriver.exe', port=9999) driver = webdriver.Firefox(service=service) Add a system environment variable NO_PROXY with the

If you want, I can tailor a troubleshooting checklist or generate a ready-to-run sample for your specific OS, Firefox, and Selenium versions.

Document the exact Firefox version, GeckoDriver version, and Selenium NuGet package versions that work together consistently. service = Service(executable_path='geckodriver

(Python example):

service = Service(GeckoDriverManager().install()) driver = webdriver.Firefox(service=service) driver.get("https://www.selenium.dev") print(driver.title) driver.quit() The most common culprits include: Cannot start the

If any link in this chain breaks, the driver service fails to start. The most common culprits include: Cannot start the driver service on http://localhost

When a test crashes or is abruptly terminated, the GeckoDriver process often continues running in the background, still holding onto its allocated port. When your next test runs, Selenium attempts to start a new driver service on a new port, but the orphaned process interferes with the initialization sequence.

Here is a review of the issue, broken down by cause, solution, and best practices.

Before diving into solutions, it’s important to understand what is failing. The Selenium WebDriver code ( FirefoxDriver ) needs a separate executable file ( geckodriver.exe ) to act as a bridge to Firefox.