Description from extension meta
FocusPrivacy is a browser extension that prevents websites from knowing if the window loses focus.
Image from store
Description from store
FocusPrivacy stops particularly invasive websites from seeing if you're on a different application or tab.
Once installed, the extension simply starts working– no configuration required.
FocusPrivacy is open source software. You can view the code here: https://github.com/AngeloD2022/FocusPrivacy