Examine source code of FA Mail

{
  "name": "FA Mail",
  "description": "This extension adds an email button to the toolbar which allows you to email the page link using your default mail client or Gmail.",
  "version": "2.0.2",
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": false
  },
  "icons": {
    "128": "128.png"
  },
  "options_page": "options.html",
  "permissions": [
    "tabs",
    "http://*/*",
    "https://*/*"
  ],
  "browser_action": {
    "default_title": "Email Now",
    "default_icon": "16.png"
  },
  "manifest_version": 2
}