Dark mode has become a mainstream expectation — most apps support it, most operating systems default to it or offer it prominently. Firefox has several layers of dark mode support, and understanding how they interact makes a difference in how consistent the experience is.

Layer 1: OS-Level Dark Mode

When you enable dark mode in Windows or macOS, Firefox respects it for its own UI: the toolbar, tabs, and settings panels go dark automatically.

This doesn't affect web pages by default — most websites have their own light/dark mode implementation that's separate from the OS setting.

Layer 2: Website Dark Mode ( prefers-color-scheme )

Well-implemented websites check the prefers-color-scheme CSS media query and serve a dark-mode version when it's set to dark .…