Ask HN: Building a browser extension for HN points for links across web

I wanted to find out if there's already, or advice on how to build, a browser extension that persistently shows across the web what the Hacker News points score is for a link. I could see this useful in Google News where before the link is clicked you already know how the HN community sees it. Or, if after you clicked on a link, what the HN votes are.