WebDriverException: Message: Can't load the profile. Possible firefox version mismatch. You must use GeckoDriver instead for Firefox 48+with Selenium

Question

I tried to follow an example how to parse websites via python and selenium. But I am running always into the following problem: calling the function webdriver.Firefox opens a firefox instance, but no website via get could be called, it seems: the whole code is blocking in function Firefox (see: print("open call never reached")) The browser is opening and after ca. 30 seconds an exception causes the broswer to exit, with message:

selenium.common.exceptions.WebDriverException: Message: Can't load the profile. Possible firefox version mismatch. You must use GeckoDriver instead for Firefox 48+. Profile Dir: /tmp/tmpl5dm_azd If you specified a log_file in the FirefoxBinary constructor, check it for details

So what do I am wrong here ? How could I set the profile right ? I tried to set marionette mode True, but got the error : "Unable to find a matching set of capabilities"

from selenium.webdriver import Firefox
from selenium import webdriver
from selenium.webdriver.firefox.options import Options
from selenium.webdriver.common.keys import Keys
from selenium.webdriver.common.desired_capabilities import DesiredCapabilities
from selenium.webdriver.firefox.firefox_binary import FirefoxBinary

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

options = Options()
options.log.level = "trace"
options.headless = True

binary = FirefoxBinary("/usr/bin/firefox")
pathDriver = "./geckodriver" 
testUrl="https://duckduckgo.com/"

print("will create firefox instance")
browser = webdriver.Firefox(firefox_binary=binary,options=options,capabilities=cap,executable_path=pathDriver)
print("open call never reached")
browser.get(testUrl)

webdriver.quit()

My test environment:

$ name -a
Linux 5.5.0-0.bpo.2-amd64 #1 SMP Debian 5.5.17-1~bpo10+1 (2020-04-23) x86_64 GNU/Linux

Also I downloaded the latest selenium and the geckodriver here see what versions I do use:

$ python3 –version
Python 3.7.3

$ pip3 freeze | grep sel
selenium==3.141.0

$ geckodriver -V
geckodriver 0.27.0 (7b8c4f32cdde 2020-07-28 18:16 +0000)

$ which firefox 
/usr/bin/firefox

$ firefox -v
Mozilla Firefox 68.10.0esr

Answer 1

When using GeckoDriver to initiate/spawn a new Browsing Context i.e. Firefox Browser session with Firefox 48+ versions, you have to use Marionette mandatorily.

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Solution

The solution would be either to work with default setting of marionette or turn marionette to True as follows:

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