For some reason there is a white line along the edge of the maximized window on the bottom, left, and right side. Also for some reason the white line is only partially on the right side. You can see in the picture it is not on the bottom part of the right side. This issue goes away when i set browser.tabs.drawInTitlebar to false in about:config, however then there's an ugly title bar at the top that ruins the dark theme. The issue does not go away when starting in safe mode with addons disabled. It goes away in f11 (fullscreen mode) but I do not like using fullscreen mode. Also, I am using a laptop (Surface Book 2 15 inch) with a second monitor (Display option: extend these displays) and the white lines only appear on maximized firefox windows on my laptop screen, not my monitor screen.