Examine source code of Stencil

{
  "applications": {
    "gecko": {
      "id": "firefox@getstencil.com",
      "strict_min_version": "48.0"
    }
  },
  "name": "Stencil",
  "description": "Instantly add text to any image - just right click!",
  "version": "2.1.2",
  "manifest_version": 2,
  "browser_action": {
    "default_title": "Stencil",
    "default_icon": {
      "19": "images/icons/logo-19x19.png",
      "38": "images/icons/logo-38x38.png"
    }
  },
  "permissions": [
    "contextMenus",
    "notifications",
    "https://local.getstencil.com/",
    "https://d34nsunniglnoy.cloudfront.net/",
    "https://d3dn9aki07x737.cloudfront.net/"
  ],
  "background": {
    "scripts": [
      "js/background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "js/extend.js",
        "js/Frame.js",
        "js/Stencil.js"
      ]
    }
  ],
  "icons": {
    "16": "images/icons/logo-16x16.png",
    "48": "images/icons/logo-48x48.png",
    "128": "images/icons/logo-128x128.png"
  }
}