Examine source code of WishList

{
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_action": {
    "default_icon": "wishlisticon128.png",
    "default_title": "+WishList.com"
  },
  "name": "Add to WishList.com Button",
  "description": "WishList.com - A button for saving wishes from any website to your wishlist at WishList.com.",
  "homepage_url": "https://www.wishlist.com",
  "icons": {
    "16": "wishlisticon16.png",
    "32": "wishlisticon32.png",
    "48": "wishlisticon48.png",
    "128": "wishlisticon128.png"
  },
  "permissions": [
    "contextMenus",
    "activeTab"
  ],
  "web_accessible_resources": [
    "*.js"
  ],
  "version": "2.91",
  "manifest_version": 2,
  "browser_specific_settings": {
    "gecko": {
      "id": "{0f50e9bc-7601-4d76-9adb-6aa11dd23c0e}"
    }
  }
}