Not work in my FF 68 (64bit).

yet another print preview that only previews first page

Tried on a few pages and it just doesn't show the whole page.
Try to grab this one for example : https://www.3dgladiator.com/tutorials/marvelousdesigner/part02/
And this extension gives you a result with 4 pages, most of the space is blank. Not convincing at all.