Hi Ellen, does it make any difference if you change among Firefox's built-in themes: Default, Light, or Dark? More info in this article: Built-in themes in Firefox - alternative to complete themes.

No. If I use one of those, it removes the "Cute cats" one that I'm using, and doesn't change the color of the main screen.

Are you using a dark theme in Windows ?

See the Release Notes.

• Changed : Built-in Firefox pages now follow the system dark mode preference
• https://www.mozilla.org/en-US/firefox/70.0/releasenotes/

Not that I'm aware of. I use a custom theme, and I haven't changed it. It's the same theme I was using before the update.

Try to set this pref to false on the about:config page.

• browser.in-content.dark-mode = false

You can open the about:config page via the location/address bar. You can accept the warning and click "I accept the risk!" to continue.

• https://support.mozilla.org/en-US/kb/about-config-editor-firefox

Did it. It didn't work.

I did a system restore and reverted to the version just before the upgrade to 70.0. I'm going to wait a bit and see if the next release changes that dark mode thing.

https://addons.mozilla.org/en-US/firefox/addon/dark-background-light-text/

That's the opposite of what I want.