The nightly builds of Firefox, which will serve as the foundation for the release of Firefox 81, introduce a new implementation of the print preview interface. The new preview interface notably opens in the current tab, replacing the existing content (the old preview interface caused a new window to open), thereby functioning similarly to Reader mode. Tools for setting up page format and print options have been moved from the top to the right panel, which also includes additional options such as controls for printing headers and backgrounds, as well as selecting a printer. A configuration setting in about:config, print.tab_modal.enabled, allows control over the new mode.
Source: opennet.ru
