Build me a cross-browser extension

I am working on a personal project which requires a proof of concept. I'd like to be able to track user engagement signals linked to a particular URL via a universal browser extension. Ideally this should be cross-browser compatible but as an MVP, it must work in Chrome. Engagement signals would include activity like tab activity, mouse scroll, keystrokes, focus and blur events etc. More detail.... Create a browser extension to track and visualise client-side browser engagement data in real-time. Ultimate aim is to determine if a user is engaged with page content and translate this into a cumulative count or duration of “engaged time”. Suggested Input Events indicating engagement to listen for: -load -focus -scroll -resize -mousemove -mousedown -keydown -mousewheel Extension should also track and record Tab activity or Focus state -Consider both whether a given browser tab is the active tab in that window ('Tab Focus') and whether the window is the active application ('Browser/Application Focus') A combination of an input occurring within the last 5 seconds and Tab activity or Focus state being active results = “engaged time” Real-time data to display within extension: -Tab Activity or Focus - Active / Inactive -Input Status - Active / Inactive -Last event tracked - event name -Count of standard time on page (dwell time on page) -Count of time with both Focus and Input active and last event having occured in last five seconds (user “engaged time” on page) event type - count event type - count event type - count event type - count event type - count event type - count event type - count event type - count event type - count Scroll Depth (nice to have)