Howto: Stop Firefox Forcing Dark Mode on Websites

Here's how to stop Firefox automatically turning on dark-mode for websites.

In the address bar, type in about:config and press ⏎ and accept the warning it gives you.

Add a new value ui.systemUsesDarkTheme set it to type number and pick one of the following:

• 0 to tell websites to always use the light theme.
• 1 to tell websites to always use the dark theme.
• 2 to tell websites you have no preference.

Dev Tools

If you want to do this on a one-off basis, open up the Dev Tools and click on the colour simulation icon to change your preferences.

It only works on a per-page basis and disappears when you refresh.

Why

I use dark mode on my laptop and most of my Linux apps. But I find most websites' dark mode to look a bit rubbish. By setting ui.systemUsesDarkTheme to 0, I get a nice looking light theme, which I can switch to dark if I want using the website's own controls.

I wish Firefox implemented this as an easy to use toggle switch - but this method works if you're happy to fiddle around in Firefox's guts.