Ask HN: see link to hacker news commentary on source page

Did some searching to no avail. Does anybody know if there is a Firefox plugin or GreaseMonkey script that, when you're on an external site that is linked to from HN, adds a link to the HN commentary for that page? For example I'm on http://supercoolbitcoinnews.example.com/omg-another-bitcoin-article and somebody has posted the url to HN, the plugin/script adds a clickable link somewhere obvious on the page so I know that there is a) already an article on HN and b) can easily go to HN and read the comments there.