python - selenium.common.exceptions.SessionNotCreatedException: Message: Unable to find a matching set of capabilities with GeckoDriver, Selenium and Firefox

Question

I have developed a python script with selenium with firefox webdriver. It is workign fine in my machine. but if i execute the same script in another machine it is giving the following error.

Traceback (most recent call last):
  File "insurance_web_monitor.py", line 13, in <module>
    driver = Firefox(executable_path='geckodriver', firefox_options=options)
  File "C:Python34libsite-packagesseleniumwebdriverfirefoxwebdriver.py",
line 167, in __init__
    keep_alive=True)
  File "C:Python34libsite-packagesseleniumwebdriver
emotewebdriver.py", l
ine 156, in __init__
    self.start_session(capabilities, browser_profile)
  File "C:Python34libsite-packagesseleniumwebdriver
emotewebdriver.py", l
ine 251, in start_session
    response = self.execute(Command.NEW_SESSION, parameters)
  File "C:Python34libsite-packagesseleniumwebdriver
emotewebdriver.py", l
ine 320, in execute
    self.error_handler.check_response(response)
  File "C:Python34libsite-packagesseleniumwebdriver
emoteerrorhandler.py"
, line 242, in check_response
    raise exception_class(message, screen, stacktrace)
selenium.common.exceptions.SessionNotCreatedException: Message: Unable to find a
 matching set of capabilities

Here is my code

import os
from selenium.webdriver import Firefox
from selenium.webdriver.common.by import By
from selenium.webdriver.common.keys import Keys
from selenium.webdriver.firefox.options import Options
from selenium.webdriver.support.wait import WebDriverWait
from selenium.webdriver.support import expected_conditions as expected
from selenium.webdriver.common.desired_capabilities import DesiredCapabilities


if __name__ == "__main__":
    options = Options()
    cap = DesiredCapabilities().FIREFOX
    cap["marionette"] = False
    options.add_argument('-headless')
    driver = Firefox(executable_path='geckodriver', firefox_options=options, capabilities=cap)
    wait = WebDriverWait(driver, timeout=10)
    driver.get('http://www.google.com')
    driver.save_screenshot(
        os.path.join(os.path.dirname(os.path.realpath(__file__)), os.getcwd(), 'screenshot1.png'))
    wait.until(expected.visibility_of_element_located((By.NAME, 'q'))).send_keys('headless firefox' + Keys.ENTER)
    wait.until(expected.visibility_of_element_located((By.CSS_SELECTOR, '#ires a'))).click()
    print(driver.page_source)
    driver.quit()

The configurations in my machine are,

Windows => 7 Professional 64-bit
Python => 3.4.4
Selenium => 3.14
Firefox => 61.0.2
geckodriver => 0.21.0

The configurations in other machine are,

Windows => 7 Professional 64-bit
Python => 3.4.4
Selenium => 3.14
Firefox => 61.0.2
geckodriver => 0.21.0

Yes every configuration is exactly same. Though this seems silly it is not working and it's torturing me. Am i missing anything to consider between the machines? Thanks in advance.

Answer 1

As per your question and code block as you are using the following Test Configuration:

• Selenium => 3.14
• geckodriver => 0.21.0
• Firefox => 61.0.2

You have to use the capability marionette mandatorily. To achieve that either:

• You can leave the capability marionette untouched as by default marionette is set to True.

• You can also specify the capability marionette as follows:

  cap = DesiredCapabilities().FIREFOX
  cap["marionette"] = True
  

---

This usecase

This error message...

selenium.common.exceptions.SessionNotCreatedException: Message: Unable to find a matching set of capabilities

...implies that the GeckoDriver was unable to initiate/spawn a new WebBrowser i.e. Firefox Browser session.

There are numerous possibilities behind the error you are seeing and can be solved through any of the following steps mentioned below:

• As you are on Windows OS you need to pass the key executable_path along with the value containing:

  • Absolute path of the GeckoDriver.
  • The Absolute path of the GeckoDriver should be mentioned through single quotes and single backward slash along with the raw (r) switch.
  • Include the extension of the GeckoDriver binary.

  • Your line of code will be:

    driver = Firefox(executable_path=r'C:pathogeckodriver.exe', firefox_options=options, capabilities=cap)
    

---

References

• selenium.common.exceptions.SessionNotCreatedException: Message: Unable to find a matching set of capabilities with Firefox 46 through Selenium
• How can Geckodriver/Firefox work without Marionette? (running python selenium 3 against FF 53)