At least on Windows, the Print button opens print preview for me. If you want to the toolbar (as opposed to having it under the Hamburger menu button, where it lives by default), you can check out the following article: Customize Firefox controls, buttons and toolbars

Hope this helps.

Thanks very much Rimas for the info about customizing the FF controls, buttons and toolbars. That was helpful of you to point out and is really good to know. But am still in need of seeing how to get my Print Preview button back : ) It appeared while had Snow Leopard, but disappeared as soon as upgraded to Mountain Lion. Thanks again for your willingness to help.

Hm, this article has Mac screenshots: How to print web pages in Firefox. So I suppose you're missing the little Preview button at the bottom of that dialog? That seems like a stock OS X thing, not something added by Firefox. I guess Apple removed that button in Mountain Lion, but hey, they have a KB article explaining how to do Print Preview now: click here to see it.

Like I said before, I'm not using a Mac, and on Windows, printing works differently: clicking the Print button opens in-browser Print preview dialog, which contains some page controls and a real Print button. If you would like to see something like that on Macs as well, reporting a bug in Bugzilla might be the right thing to do.

Mountain Lion was released in 2012, so I suppose there might be advice in old threads or on the Apple forums if you don't get a response here right away.

Thank you to both Rimas and jscher2000 - - very helpful!!