I do not find the "Print" feature in the menu nor elsewhere for the Firefox for Android. Is printing to a home printer an option?
It's not ready yet, but check the Share menu. You should be able to save to PDF and then print it from PDF reader.
I installed the Samsung Print Service Plugin on my tablet, a Samsung S7+. Now, I can Share to that plug-in to print.
I'm not certain this will work on a non-Samsung device but it's worth a try.