Firefox will soon begin respecting Windows 10’s dark app mode setting. But you can enable dark mode in Firefox today, on any operating system, and without installing any third-party themes. This works on Windows 7, Windows 10, macOS, and Linux.
To change your Firefox theme, click menu > Add-ons in Mozilla Firefox.
Click “Themes” at the left side of the add-ons page.
You’ll see three pre-installed themes here: Default, Dark, and Light.
The Default theme is a standard light theme that respects your Windows theme settings. For example, if you enable colored title bars on Windows 10, Firefox will use colored title bars with the default theme.
The Dark theme is Firefox’s dark mode. Everything in Firefox—-including the title bar, toolbars, and menus—will turn black or a dark shade of gray with the dark theme.
The Light theme uses lighter grays. When you enable this theme, Firefox will use a light gray title bar and other elements, even when you have colored title bars enabled in Windows.
To enable the Dark theme or any other theme, click the “Enable” button to the right of it. Firefox’s theme will instantly change.
You can install more themes from the Themes section of the Mozilla Add-ons website.
If you’ve enabled Firefox Sync, your selected theme will be synchronized to any other computers on which you’ve signed into Firefox. To view your Firefox Sync settings, click menu > Options > Firefox Account.