This repository can build a docker image containing geckodriver and Firefox. It also contains a docker-compose file to orchestrate running them against Xvfb, with x11vnc.
Run docker-compose up, and geckodriver will listen on port 4444. x11vnc
will listen on port 5900.
Currently geckodriver 0.28 is installed along with the latest Firefox package from Debian sid.
To add extra certificates, preferences etc., see the geckodriver documentation for how to set the Firefox profile via WebDriver capabilities: https://github.com/mozilla/geckodriver#capabilities-examples