Examine source code of Inbound Mail

{
  "version": "1.0.0",
  "manifest_version": 2,
  "name": "Inbound Mail",
  "description": "Take back control of your emails.",
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "lib/js/browser-polyfill.js",
        "content.js"
      ]
    }
  ],
  "background": {
    "scripts": [
      "lib/js/browser-polyfill.js",
      "background.js"
    ]
  },
  "browser_action": {
    "default_icon": "img/email.png",
    "default_popup": "popup.html"
  },
  "permissions": [
    "tabs",
    "storage"
  ],
  "icons": {
    "128": "img/email.png"
  }
}