Hi everyone, I haven't tried this myself, but it might be the case that our new sandboxing engine for the beta always-on tasks feature might support Chrome/chromedriver and newer Firefoxen/geckodriver.
Ping us a note here or by email and we'll switch it on for you if you want to give it a go?
You'll need to figure out how to download firefox and chromedriver binaries into your home folder, and how to tell selenium to use those binaries instead of the system-installed ones, but you might have a chance... Hey even phantomjs might work!