Can you provide links to sites with this issue so that we can try to replicate? What OS? What Desktop? Are you on Wayland or X11? Try downloading another copy of Firefox and run it from the folder. Do not sign into your Firefox account and see if you have the same issue.

https://www.mozilla.org/en-US/firefox/all/#product-desktop-release

Operating System: openSUSE Tumbleweed 20220113 KDE Plasma Version: 5.23.5 KDE Frameworks Version: 5.90.0 Qt Version: 5.15.2 Kernel Version: 5.16.0-1-default (64-bit) Graphics Platform: X11 Processors: 4 × Intel® Core™ i7-4810MQ CPU @ 2.80GHz Memory: 31.0 GiB of RAM Graphics Processor: Mesa DRI Intel® HD Graphics 4600

You can change this pref on the about:config page from 3 to 2 to revert to the Firefox 94 behavior.

• layout.css.prefers-color-scheme.content-override [dark:0, light:1, system:2, 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