Ctrl+p instead of Alt+p for Windows users would be great!
Thank you!

After testing on various sites It seems to only work well with The Guardian. A few articles I tested on The Guardian laid out consecutively on pages adding Topics at the bottom. The other sites tested left gaps, empty pages altogether, and in some no content.

Sites tested: makeuseof.com, outsideonline.com, bloomberg.com, narratively.com,scientificamerican.com

Windows 10 | Firefox 69.0b6 (64-bit)

Does the job, but could be improved: Background colors and images are hidden by default, and there’s no option in the preview interface to show them. Also, clicking Landscape doesn’t change the preview (although it does change the setting, so you will get a landscape-format print).

Handy! The printer icon appears in the address bar, providing very intuitive access, also saving room for adding other extensions/buttons in the actual Firefox toolbar.

Exactly what I was looking for. Preview works very well! Thanks! Don't know why this isn't a feature built into Firefox like other browsers.