Print TO file, not print a file. Print TO file is to take a screenshot of a page or document to avoid any interpretation issues later.

To print A file, Android has a generic printer driver and there are more featureful proprietary drivers. I printed a shipping label from my phone over wifi the other day. Very easy to detect and add a printer.

It printed slowly and only printed half the page on the first try, but out of the typical printing experience, that's not too bad.

I don't think you can from Firefox directly: https://github.com/mozilla-mobile/fenix/issues/10217

So, probably save as PDF, then print PDF.

With a network printer for example.