Think Google Docs, Hangouts and G Suite Don’t Work with Firefox? Think Again (blog.mozilla.org)

Printing in Google Docs is only possible through downloading a PDF file. I believe this is by Google's choice and not a Firefox limitation. It is a little bit annoying, but doesn't stop me from using Firefox.

In detail, pressing CTRL/CMD+P:

- in Firefox, brings a Google Cloud Print popup with an option to download a PDF

- in Chrome, brings a regular system print modal