Websites backgrounds in userChrome.css

[4n0nct]

Is there a way (by selecting ourself our global colors in firefox menu) to achieve web pages transparency by keeping text and images in full opacity ? With few lines defining background (tabs, webpages, menus, right-click menus) ?
Edit: I've tried to understand the infos in:
https://medium.com/web-dev-survey-from-kyoto/glassmorphism-for-firefox-2113dff03747
But I'm not smart enough to understand how to deal with all that by myself.