A Racket library that lets you control Firefox via the Marionette Protocol.

Install marionette:

$ raco pkg install marionette 

Run Firefox with the -marionette flag:

$ /path/to/firefox -headless -marionette -safe-mode 

Run this script:

#lang racket (require marionette) (call-with-browser! (lambda (b) (call-with-page! b (lambda (p) (page-goto! p "https://racket-lang.org") (call-with-page-screenshot! p (lambda (data) (define filename (make-temporary-file "~a.png")) (with-output-to-file filename #:exists 'truncate/replace (lambda () (write-bytes data))) (system* (find-executable-path "open") filename)))))))

To run a headless, marionette-enabled Firefox while you've got another instance of the browser open, add the -no-remote flag:

$ /path/to/firefox -no-remote -headless -marionette -safe-mode 

It's advisable that you use a separate profile as well:

$ /path/to/firefox -P marionette -no-remote -headless -marionette -safe-mode 

You can create new profiles by visiting about:profiles in the browser.