The printer icon seems to function as print-preview.

Hi there mawallace, the printer icon does bring up print-preview. As I'm sure you know after it brings that up you can click print and it will print. If you want to bypass this there are a few things you can do. All of this will be for windows as I do not have a Mac. You can press Alt go to file, then click on print. That will not bring up print-preview. You can also press Cntrl and P. That will also print and not bring up print-preview.

But I want to hit an icon and print - I do not want to have to do a shortcut - as I used to do!

That is ok, you can go to file and print. If you go to the three line icon and click customize you can make it so that file will always be there. You gut click on the three line icon. Then click customize. Then near the bottom left click show/hide toolbars. Click on that then click on menu bar.

Doesn't work for me. Just want to click on the Printer Button to "Print...", like how it used to work.

I can understand. Unfortunately I think that is the best we can do right now. If you would like you can give your feedback to Mozilla here. Everyone here is a volunteer dedicated to helping users. If you give feedback at the link I gave you. It will go to the people that get to make decisions about how Firefox looks and works.