Hola Entiendo que tienes un tema especifico cargado, no uno por defecto en el Firefox, algunos usuarios comentan que si el tema tiene tonos fuera de los claros todo los menús del Firefox (y posiblemente la navegación) se vuelven a modo oscuro. Entiendo que es un problema de la nueva versión, la solución momentánea sería elegir un tema mas claro, mientras tanto busco si hay un bug declaro y su posible solución. Saludos

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. It also signals sites that you have a dark theme preference.

What to do about this

(1) For people not attached to their toolbar theme

The fastest workaround for now is to change your toolbar 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 a pastel 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/

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

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

This is only a partial workaround for the built-in pages, and for websites that have light/dark responsive themes. (This is the middle panel of the attached screenshot.)

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/Return 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.