There is a game called csgo with in-game items which are used by a lot of people to trade with.
I made a website in which you enter an inspect link (a link which usually opens the game and shows the item) and takes a screenshot of the item.
The Addon does the following: It looks for those kinds of links in websites and makes it, so when you click on it you get a small popup which gives you the choice to either open the game as usual or open the link with my website.
A couple examples of sites with links like that are:
http://steamcommunity.com/market/listings/730/%E2%98%85%20Karambit%20%7C%20Night%20(Battle-Scarred) (click on the grey 'inspect in game' button)
https://opskins.com/?loc=shop_search&app=730_2&search_item=%22Bayonet%22 (click on any of the orange inspect buttons)