Hi Mykola,

there is already a bug[1] for firefox. Geckodriver has to be shippet
with firefox not with python-selenium. Until that you have to use a
other one e.g. chromium-driver as described in
NEWS.debain/README.debian. Alternative yo have to install the
Geckodriver manually[2].

Regards
Sascha

[1] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=874207
[2]
https://askubuntu.com/questions/851401/where-to-find-geckodriver-needed-by-selenium-python-package