Running a 64-bit geckodriver against a 32-bit version of Firefox (or vice versa) frequently causes the background process to fault instantly upon being invoked by C#.

service = Service(executable_path='geckodriver', port=7056)

Check Task Manager (Windows) or Activity Monitor (macOS) for any running geckodriver or firefox processes and terminate them before restarting your test.

Ensure Selenium is installed in the same environment where you run the script.

firefox --version

When attempting to run a Selenium test using Firefox as the browser, the test fails to start the driver service on http://localhost . This issue prevents the test from executing successfully.

Sometimes Selenium cannot find Firefox or the driver, even if they are in default locations. Explicitly defining them in your C# code often resolves this:

The driver service may take longer to initialize than the default or manually set timeout allows. Step-by-Step Solutions 1. Explicitly Specify the GeckoDriver Path