title: WebDriverException: Message: invalid argument: can't kill an exited process with GeckoDriver, Selenium and Python on RaspberryPi3
body: <p>Server: Raspberry Pi 3<br>
  OS: Dietpi - version 159<br>
  Geckodriver version: 0.22 for arm<br>
  Firefox version: 52.9.0<br>
  Python version: 3.5<br>
  Selenium version: 3.14.1  </p>
  
  <p>Gecko is executable, and is located in /usr/local/bin/</p>
  
  <pre><code>from selenium import webdriver
  from selenium.webdriver.common.by import By
  from selenium.webdriver.support.ui import WebDriverWait
  from selenium.webdriver.support import expected_conditions as EC
  from selenium.webdriver.firefox.options import Options
  import time
  
  
  
  options = Options()
  options.set_headless(headless=True)
  driver = webdriver.Firefox(firefox_options=options)
  
  print('Need your login credential')
  username = input('What is your username?:\n')
  password = input('What is your password?:\n')
  ...
  ...
  </code></pre>
  
  <p>Output:</p>
  
  <pre><code>root@RPi3:~# python3.5 ITE-bot.py 
  Traceback (most recent call last):
    File "ITE-bot.py", line 12, in &lt;module&gt;
      driver = webdriver.Firefox(firefox_options=options)
    File "/usr/local/lib/python3.5/dist-packages/selenium/webdriver/firefox/webdriver.py", line 174, in __init__
      keep_alive=True)
    File "/usr/local/lib/python3.5/dist-packages/selenium/webdriver/remote/webdriver.py", line 157, in __init__
      self.start_session(capabilities, browser_profile)
    File "/usr/local/lib/python3.5/dist-packages/selenium/webdriver/remote/webdriver.py", line 252, in start_session
      response = self.execute(Command.NEW_SESSION, parameters)
    File "/usr/local/lib/python3.5/dist-packages/selenium/webdriver/remote/webdriver.py", line 321, in execute
      self.error_handler.check_response(response)
    File "/usr/local/lib/python3.5/dist-packages/selenium/webdriver/remote/errorhandler.py", line 242, in check_response
      raise exception_class(message, screen, stacktrace)
  selenium.common.exceptions.WebDriverException: Message: invalid argument: can't kill an exited process
  </code></pre>
  
  <p>Any idea what is wrong? I've tried google without luck.</p>