Examine source code of Nullmail Extension

{
  "manifest_version": 2,
  "name": "Nullmail Extension",
  "version": "1.1",
  "permissions": [
    "storage",
    "contextMenus",
    "webRequest",
    "tabs",
    "https://www.nullmail.cc/*",
    "https://nullmail.cc/*"
  ],
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": true
  },
  "browser_action": {
    "default_title": "Nullmail Extension",
    "default_icon": {
      "16": "icon16.png",
      "32": "icon32.png",
      "48": "icon48.png",
      "128": "icon128.png"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "nullmail-extension@nullmail.cc"
    }
  },
  "icons": {
    "16": "icon16.png",
    "32": "icon32.png",
    "48": "icon48.png",
    "128": "icon128.png"
  }
}