Examine source code of Twatter

{
  "manifest_version": 2,
  "name": "Twatter",
  "description": "Filter Twitter Feed",
  "version": "1",
  "icons": {
    "128": "128.png"
  },
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": false
  },
  "permissions": [
    "storage",
    "https://twitter.com/",
    "https://mobile.twitter.com/",
    "webNavigation"
  ],
  "browser_action": {
    "default_popup": "popup.html",
    "default_title": "Twatter",
    "default_icon": "128.png"
  },
  "content_scripts": [
    {
      "matches": [
        "https://twitter.com/*",
        "https://mobile.twitter.com/*"
      ],
      "js": [
        "twatter.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "twatter@betafunk.dk"
    }
  }
}