firefox --version If this fails, Firefox cannot be found in your PATH .
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: firefox --version If this fails, Firefox cannot be
sudo apt-get install xvfb xvfb-run python your_selenium_script.py Or, use PyVirtualDisplay in Python: firefox --version If this fails
from selenium import webdriver from selenium.webdriver.firefox.service import Service service = Service(executable_path=r'C:\drivers\geckodriver.exe') driver = webdriver.Firefox(service=service) your Firefox automation will start cleanly