Cannot Start The Driver Service On Http Localhost Selenium Firefox C [better] Jun 2026

If you frequently stop your test executions abruptly via the IDE (e.g., stopping the Visual Studio debugger mid-test), the driver.Quit() method is bypassed. This leaves orphan geckodriver.exe and firefox.exe processes running invisibly in the background. Eventually, these processes can lock up system resources or conflict with new port allocations.

If you're an automation engineer working with Selenium WebDriver in C#, you've likely encountered this frustrating exception at some point: If you frequently stop your test executions abruptly

Security software or windows firewall configurations can block the internal HTTP traffic between your C# test script and geckodriver.exe . stopping the Visual Studio debugger mid-test)