This is a browser extension that plays the Wii Shop Channel theme in the background when you visit a shopping website. You can also select the music from the 3DS eShop, DSi Shop, Wii Shop Banner/Home, Wii U eShop, and Coconut Mall.
The extension only requires two permissions: Tabs, to check the URL of the currently-active tab, and Notifications, to show a message after the extension is installed.
This extension is not developed by, or affiliated with, Nintendo in any way.