The new print interface has been progressively released to a subset of users over multiple releases. It's only gone to 100% of users as of Firefox 86.

I guess I was in the early rollout. I was in the middle of designing a print layout about a month or two ago when firefox got updated. After a restart I suddenly was missing the print preview option in the menu to test my design. I was really glad to see that I could from now on just press Ctrl + P and get a much better experience.

it does not work here the `print.tab_modal.enabled` preference to `false´ fix described below helped