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

What to do about this

The fastest workaround for now is to change your theme to one that uses light/white text. By light text I mean, for example, the built-in Dark theme, or an add-on theme with white or light text on the tabs such as:

https://addons.mozilla.org/firefox/addon/dark-fox-18066/

I have attached a screenshot illustrating the difference between a theme with light text on the tabs and dark text on the tabs.

Does that work for you?

Hi there,

In my post here: https://support.mozilla.org/en-US/questions/1360389?page=2#answer-1479952

I explain about a solution for forcing Firefox to use a Light theme. Since you're looking to do the opposite and use a Dark theme, it'll be the same process but just use a value of 0 instead of 1 (as my post explains).

Hope this helps!

-CB