selenium-check

Install latest stable Firefox version (https://www.mozilla.org/pl/firefox/new/)
Download latest gecko driver version for your OS (https://github.com/mozilla/geckodriver/releases)
Unpack gecko driver

tar -xvzf geckodriver*

Move gecko driver file to /usr/local/bin/ directory

cp geckodriver /usr/local/bin/

Install selenium (best practise in python virtualenv)

pip install -U selenium

Run test from selenium-check repository

cd selenium-check
python test.py

You should see stxnext.com on new firefox instance