As you discovered, 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

The fastest workaround for now 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/

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

Background / Other Settings

Firefox 95+ is taking more and more cues from your toolbar area theme for how to style other aspects of the browser. There is a setting for some of these, but not all of them.

(A) Right-click context menus, toolbar drop-down panels

Starting in Firefox 89, these would flip to a dark background if the text on the inactive/background tabs was white or light. Firefox 96 has extended this adaptation to more parts of the browser. As far as I know, the only built-in way to avoid this is to change your toolbar theme to one with dark text on the inactive/background tabs. (The other way is the not-officially-supported userChrome.css file route.)

(B) Built-in pages, and websites that have light/dark responsive themes

Starting in Firefox 95, Firefox would inform pages that you preferred a light/dark theme based on your Firefox toolbar theme instead of your system theme. There is a way to decouple your page (content) theme preference from your toolbar theme. At this point, it's only available 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 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.

Thank you, all my doubts are cleared. That was very detailed.

This worked for me as well. Whew. It was driving me to distraction.

I just hate this. Once again, Mozilla has unilaterally, out of the blue, applied substantial changes to the interface that just are not workable, so that I have to drop everything in the middle of my work day and take time that I really need to be spending on other things adjusting my primary work tool so it is usable again. Not only was my theme suddenly changed to dark without notice, borders have been removed from EVERY SINGLE THEME I had previously identified and saved specifically because the borders on background tabs were easy to see, and apparently for every other theme as well.

Who the heck is making these decisions?? Do they have any clue at all that what is aesthetically pleasing to them is NOT some universal norm that should be abruptly implemented with no notice, input, or option to decline on a tool that people are using hundreds of times a day?? Do they have any respect at all for the time of FireFox users? Clearly not on both counts. SO SICK OF THIS!!!!!!!

Not only was my theme suddenly changed to dark without notice, borders have been removed from EVERY SINGLE THEME I had previously identified and saved specifically because the borders on background tabs were easy to see, and apparently for every other theme as well.

If you choose a toolbar theme with dark text, you'll get dark text on a light background elsewhere in the browser. The idea behind this change was to match your intent for how you like to view the world (light-on-dark or dark-on-light). The mistake was to interpret something many users consider purely decorative as an accessibility preference. Hopefully we'll have a setting in the future to decouple your toolbar theme color scheme from everything else.

Regarding borders on background tabs, we lost them in Firefox 89's Proton redesign. If you need help with that, it's now a userChrome.css hack. We can have a separate thread on that if you want to dive into it.

You guys do realize this "coupling" of custom theme and dark/light mode is unacceptable, right?

I need all my menus to be light background and dark text. I had - operative word HAD - a preferred theme I have used for YEARS with my favorite anime character that had white text on a beautiful shade of blue for the buttons... that didn't do a thing to my menus, etc. I tried disabling Proton when it came out. It worked for a while. Every time Firefox pushed through a downgrade... 94... 95... now 96... I have had to waste a ton of time getting my browser usable again.

Today I had to say goodbye to my theme because I couldn't find a way to make my menus viewable and non-headache-inducing without forcing a "light theme". I am quite angry and upset about this.

Kill Proton. Kill dark theme. And give the users control and choice over these options. Firefox is still better than Edge or Chrome (which has earned its nickname Guaranteed Crash). But I'm really getting tired of having my chain jerked so much.