Examine source code of SecureMail Encryptor

{
  "manifest_version": 2,
  "name": "__MSG_extensionName__",
  "version": "1.0",
  "description": "__MSG_extensionDescription__",
  "icons": {
    "16": "icons/icon16.png",
    "48": "icons/icon48.png",
    "128": "icons/icon128.png"
  },
  "browser_action": {
    "default_popup": "popup/popup.html",
    "default_icon": "icons/icon48.png"
  },
  "permissions": [
    "storage",
    "activeTab",
    "https://mail.google.com/*",
    "https://outlook.live.com/*",
    "https://mail.yahoo.com/*"
  ],
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": false
  },
  "options_ui": {
    "page": "options/options.html",
    "open_in_tab": true
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{acc53857-ba34-4107-9312-accce7bbcef3}"
    }
  }
}