Sorry, what is "black screen mode"? Is that a dark theme for Windows 10, or do you mean a command window (like the old "DOS" days)? What do you mean here: "how-to fixed vga mude enabled and ithng format all program". ? If Firefox is not running at the same resolution as your system, check whether there's a bad compatibility setting. To do that, find the icon you use the start Firefox, and either: * Right-click a desktop shortcut, then click Properties * Right-click a Firefox icon pinned to the Taskbar then right-click Mozilla Firefox, then click Properties You should clear all the boxes on the Compatibility tab for best results (giant screenshot below). <img src="https://prod-cdn.sumo.mozilla.net/uploads/images/2018-07-25-13-24-46-baad8f.png"> Any difference the next time you start Firefox?