This has been an issue for a long time. I’ve been trying to avoid Chromium based browsers, but Firefox seems to be unable to print a lot of web pages without cutting off the content between pages. This is Firefox specific, as it doesn’t happen with Chromium browsers. It’s really a pain in the ass when I need to print something I have to open another browser and print it from there. I see tons of complaints about this online going back for years. I just spent the past two hours trying (unsuccessfully) to print a recipe correctly. I eventually gave up, opened Edge and printed from there. The current state of web browsers is dogshit. It’s either give up all of your privacy or use broken stuff. Neither is good.
As others already have mentioned, the issue might only be partially firefox’s fault. Meaning that webpage that wants to be printable should normally have to provide a print layout and if it doesnt then it is up to the browser to make a best guess at how to render it correctly for printing. Sadly the modern web has a huge amount of web content (sticky headers, floating elements, shadow/hidden elements, and so on) that can make it really hard to interpret pages suitable for printing.
That said, that doesnt mean that there is no room for improvement to firefox’s “best guess”.