Yes, in Firefox printing is rather rudimentary in comparison with most other web browsers, except on Mac OSX.

In Windows & most Linux 'flavors" when you initiate printing via the standard keyboard command of { Ctrl + P } you get what is known as the native print dialog where you can open Preferences to the right of Printer > Name. That dialog window will also appear after you leave the Print Preview window if you are using a Toolbar button to initiate printing.

Then using that Preferences button what you will see is the printer driver software window for the selected Printer; that is where the Black & White option will appear.

I checked that and there is no option to choose black & white or color.

Hi, yes they did a change in the Printer part some time ago it seems. I just noticed a week ago. You may have to add a Extension on to get back full control of Print. https://addons.mozilla.org/firefox/search/?platform=windows&q=print

So, if you can't change the printer properties to force grayscale, you could consider changing the page by injecting a "grayscale" style rule. That will flip it from color to grayscale.

Here's how you set it up: you install the script to your Bookmarks Toolbar or Bookmarks Menu, somewhere convenient that you can access when you way to gray a page. You can install from here:

https://www.jeffersonscher.com/res/sumomarklets.html#GrayTog

Here's an old screenshot showing the result of using it on that page:

Full size: https://prod-cdn.sumo.mozilla.net/uploads/images/2017-07-08-10-19-47-090d11.png

Note: Most pages will allow this, but some have rules against external scripts, in which case unfortunately it won't work; you would need a "real" add-on (maybe there is one?).