Also, I recently stumbled across the "Adaptive Tab Bar Color" Plugin, which colors the tab bar based on the dominant color of the current website.
https://addons.mozilla.org/en-US/firefox/addon/adaptive-tab-bar-colour/
addons.mozilla.orgAdaptive Tab Bar Color – Get this Extension for 🦊 Firefox (en-US)Download Adaptive Tab Bar Color for Firefox. Changes the color of Firefox theme to match the website’s appearance.