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

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.

When you write a Selenium script, the following happens behind the scenes:

When automated tests crash or are force-closed, the background geckodriver.exe or firefox.exe instances often continue running in the background. These zombie processes lock the localhost ports that a new test execution requires, causing the driver service to immediately fail on startup.

dotnet add package Selenium.WebDriver dotnet add package Selenium.WebDriver.GeckoDriver Use code with caution.

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Solving the "Cannot start the driver service on http://localhost" Error in Selenium C# for Firefox

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options = Options() options.add_argument("--headless") options.set_preference("browser.download.folderList", 2)

Then download the latest geckodriver and install latest Firefox. These zombie processes lock the localhost ports that

To resolve the " Cannot start the driver service on http://localhost

When using C# with GeckoDriver (Firefox), this message typically indicates that Selenium is trying to launch the browser but cannot establish a connection with the driver executable itself, not necessarily Firefox, but the bridge between your code and the browser.

var driver = new FirefoxDriver(options);

Always implement proper disposal patterns to prevent resource leaks: This link or copies made by others cannot be deleted

Disable or proxy settings that might redirect local traffic.

executable, or resource exhaustion from too many orphaned driver processes. Stack Overflow 1. Correct the Driver Service Path

If this fails, Firefox cannot be found in your PATH .