Great article! I'm the product manager for the headless feature, and I'm unsure why `binary.add_command_line_options('-headless')` doesn't work for you, as the flag does work when invoking Firefox directly:

> "c:\Program Files\Nightly\firefox.exe" -headless

(It also works when Firefox is invoked from a Node.js script in a test suite for a Node.js program that drives Firefox.)

Perhaps this is a Selenium issue?