Hello, I'm sharing this bit of knowledge as it was not obvious at all. Selenium is hard-coded to look for 'firefox' in a couple places, even in the serialized settings it sends to the browser instance controlled by geckodriver.
Here's the initialization that worked using Guix on the core-updates-frozen-batched-changes branch (where 'geckodriver' was recently added to IceCat): --8<---------------cut here---------------start------------->8--- from selenium.webdriver import Firefox, FirefoxOptions # Monkey patch the KEY string for IceCat. FirefoxOptions.KEY = "moz:icecatOptions" options = FirefoxOptions() options.headless = False options.binary = 'icecat' options.set_capability('browserName', 'icecat') self.driver = Firefox(options=options)# TODO: --8<---------------cut here---------------end--------------->8--- The non-obvious was monkey patching the 'moz:icecatOptions' string of the FirefoxOptions object, and having to set the 'browserName' capability; otherwise a capability/invalid argument execption would be raised. If you use chromedriver (included with) our ungoogled-chromium instead, it is more straightforward as there is nothing to rename/monkey patch: --8<---------------cut here---------------start------------->8--- options = ChromeOptions() options.headless = False self.driver = Chrome(options=options) --8<---------------cut here---------------end--------------->8--- I hope that helps someone else :-). Maxim