So many PDF converters

UPDATE: For a new roundup as of June 2020, see:

This is a little roundup showing some initial movement toward using the new API among the Firefox57-tagged extensions. I'm sure I'm missing things, but this took long enough already. ;-)

Uses the built-in saveAsPDF() function (Firefox 56+ on Windows and Linux):

Uses an online service:

Not a direct PDF converter:

To me, the presence of conversion tools for Mozilla is, quite the contrary, way poorer than for Chrome, as I see. And I’m not talking bout crappy ones. I prefer to use the online apps for such purposes, this one by PDFfiller as well: I need such a thing just for case of editing reports and filling forms, so its features are fine enough. But speaking of add-ons for Firefox directly, PDF editor online hands down the very best one

This thread is about add-ons for converting the currently displayed web page to a PDF. I don’t think the site you mentioned does that.

Looks like there’s a new one and it’s from Adobe supposedly: PDF Print & Save

Just what I was looking for, thank you.
Though I have to say, I did not read further than " My own extension" and installed yours.