Found the solution: In private mode, right-klick the title bar, select "Customize Toolbar", select "Manage Themes" at the bottom of the browse window, enable the "Light-Theme" in the "Manage your Themes"-Section of the settings.

Seems as if Firefox is enabling the dark theme für private browsing mode windows by default with the recent update, but is not communicating this change.

I will try this, but, how do I get to "Private Mode"?

You can set browser.theme.dark-private-windows = false on the about:config page.

You can open the about:config page via the location/address bar. On the warning page, you can click "Accept the Risk and Continue"to open about:config.

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

You can set browser.theme.dark-private-windows = false on the about:config page. You can open the about:config page via the location/address bar. On the warning page, you can click "Accept the Risk and Continue"to open about:config.

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

Thanks a lot!

Is this doing the same as when I enable the "Light-Theme" in the "Manage your Themes"-Section of the settings as I mentioned? If I check the browser.theme.dark-private-windows - setting in the config-page it's on "true" and still my firefox appears the the light-theme when using private mode as shown in the attached screenshot. So this configuration setting seems to be overwritten by the themes-configuration?

I will try this, but, how do I get to "Private Mode"?

right-click firefox icon, select "new private window"