I wouldn't say that Firefox specifically is worse at it than other browsers though, but I kind of agree with parent comment that the "new web" doesn't care about printing.
On more and more pages I encounter issues like the printer only printing out the cookie warning window, or just the left navigation bar, etc. and none of the actual page content that I wanted to print. Or content goes up to the first in-line advertisement and then cuts of there with just blank pages coming out of the printer after that. Or weird pagination issues where there's text on page 1 and text on page 2, but there's a bunch of text missing in between that is otherwise visible fine on the screen.
I'm talking about web pages that don't specifically have a "print" button on them. If it looks like the page is using a fancy layout I typically now just do a screenshot and print the resulting .png.
Print in firefox is totally broken. The change to Chromium was the last nail in the coffin for printing. The new web does not care.