It is possible you selected one of the Colorways themes that are included in Firefox. You can find the built-in themes (light, dark, system) and further down the Colorways themes included in Firefox on the "Add-ons and Themes" page (Ctrl+Shift+A; Themes tab). *https://support.mozilla.org/en-US/kb/personalize-firefox-colorways *https://support.mozilla.org/en-US/kb/use-themes-change-look-of-firefox *https://blog.mozilla.org/en/products/firefox/introducing-new-colorways-for-firefox-94/ Start Firefox in <b>Troubleshoot Mode</b> to check if one of the extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) or if <b>hardware acceleration</b> or <b>userChrome.css</b> is causing the problem. *switch to the DEFAULT theme: "3-bar" menu button or Tools -> Add-ons -> Themes *do NOT click the "Refresh Firefox" button on the Troubleshoot Mode start window *https://support.mozilla.org/en-US/kb/diagnose-firefox-issues-using-troubleshoot-mode *https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems