https://developer.chrome.com/docs/extensions/mv2/background-pages
Manage events with background scripts | Manifest V2 | Chrome for Developers
Sep 17, 2012 - How to respond to browser triggers (events) from a Chrome Extension background script.
chrome for developersmanage eventsbackground scriptsmanifestv2
https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/Background_scripts
Background scripts - Mozilla | MDN
Background scripts or a background page enable you to monitor and react to events in the browser, such as navigating to a new page, removing a bookmark, or...
background scriptsmozillamdn