Maybe check the default colors in Settings.

• Settings -> General: Fonts & Colors -> Colors

I hate the black background - bad for my eyesight. Wish I knew how to change it before it makes me blind.

@classicalschooling

You can look for an extension on the Add-ons website.

• Dark Reader https://addons.mozilla.org/firefox/addon/darkreader/

it seems to me Dark Reader add on would make EVERY page BLACK! i want EVERY page WHITE

You can change this pref on the about:config page from 3 to 2.

*layout.css.prefers-color-scheme.content-override
Dark (0), light (1), system (2) or browser (3)

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

I did the about:config change but still had some black backgrounds. It seems this kind of problem was introduced when Mozilla started using Proton. I am installing version 88 which was just before they started using it until they make it much easier to get rid of black backgrounds.

I did the about:config change but still had some black backgrounds.

You mean in Firefox 96, I assume.

With yesterday's update, Firefox now harmonizes more panels 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. It also signals sites that you have a dark theme preference.

What to do about this

The fastest workaround 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 such as:

https://addons.mozilla.org/firefox/addon/firefox-b/

Visit the page, install, you can be done in 30 seconds.