Google uses a cookie to store your dark mode preferences. Firefox may delete this data every time you close the browser, depending on your settings. To prevent this: 1. Go to ☰->Settings->Privacy & Security 2. Under Cookies and Site Data, uncheck the box for "Delete cookies and site data when Firefox is closed" 3. Go to Google again and turn off dark theme like you did before Now Google should remember your preference for a light theme.

Is Google the only page that defaults to dark mode or does it affect other sites and internal Firefox pages?

-- For Reference if Relevant --

What is happening in Firefox 96

Firefox 96 now harmonizes more parts of Firefox with your toolbar theme. When the text color on your background tabs is light/white, it triggers Firefox to use a dark background on menus, the sidebar, the Library window, and various built-in pages. Firefox also signals sites that you have a dark theme preference.

What to do about this now

(1) Changing your toolbar theme is a quick fix

The fastest workaround for now is to change your theme to one that uses dark text. By dark text I mean, for example, the built-in Light theme, or an add-on theme with black or dark text on the tabs. That doesn't need to be blinding, it can have some color. As examples:

• Firefox Logo: https://addons.mozilla.org/firefox/addon/firefox-b/
• Winter snow: https://addons.mozilla.org/firefox/addon/blue-winter-snow/
• Green shoots: https://addons.mozilla.org/firefox/addon/printania/
• Great wave: https://addons.mozilla.org/firefox/addon/japan-style-kanagawa-gr-232767/
• Kitten: https://addons.mozilla.org/firefox/addon/savage-black-kitten/

(2) For people who can't part with their toolbar theme

This is a partial workaround for the built-in pages, and for websites that have light/dark responsive themes.

Currently, the only way to decouple your page (content) theme preference from your toolbar theme is through the back door:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button accepting the risk.

More info on about:config: Configuration Editor for Firefox. The moderators would like us to remind you that changes made through this back door aren't fully supported and aren't guaranteed to continue working in the future.

(2) In the search box in the page, type or paste layout.css.prefers-color-scheme.content-override and pause while the list is filtered

(3) Double-click the preference to display an editing field, and change the value to whatever you prefer from the list below, then press Enter or click the blue check mark button to save the change.

• 0 => Force a Dark background
• 1 => Force a Light background
• 2 => Follow the System theme (default in Firefox 94)
• 3 => Follow the Browser toolbar theme (default in Firefox 95+)

The about:config page should immediately reflect your saved change.

What about other aspects of the UI?

For the sidebar, menus, and toolbar drop-down panels, there is an unofficial, community-supported option, which is to override the built-in styles using your own style rules in a userChrome.css file. I think people are still pondering how to do that efficiently, and perhaps you aren't that into hacking your browser anyway.

thank you for all solutions. i changed the key into 2 in stead of 3. it seems to work.