I am using the current version of Firefox in Mac OSX Yosemite 10.10.1. As I am also using Firefox on Windows, I am used to being able to generate a print preview via the File -> Print preview command. On Mac OSX this command is missing. Is there a way to do this on Mac?
Click File > Print (or ⌘+P) and then click the PDF menu and choose the first option "Open PDF in Preview". That gives you a preview of what the printout will look like. I wasn't able to verify, but it looks like the PDF a temporary file, and will automatically be cleaned up. So it's not cluttering up your system.
Otherwise, this addon might do the trick https://addons.mozilla.org/en-US/firefox/addon/printprint-preview/