Examine source code of Focussed Twitter

{
  "name": "Focussed Twitter",
  "version": "0.1",
  "short_name": "focussedtwitter",
  "description": "Let's focus on the tweets!",
  "manifest_version": 2,
  "content_scripts": [
    {
      "run_at": "document_start",
      "matches": [
        "https://twitter.com/*",
        "https://mobile.twitter.com/*"
      ],
      "css": [
        "styles/focussed-twitter.css"
      ],
      "js": [
        "scripts/focussed-twitter.js"
      ]
    }
  ],
  "background": {
    "scripts": [
      "scripts/background.js"
    ],
    "persistent": false
  },
  "permissions": [
    "declarativeContent",
    "storage"
  ],
  "browser_action": {
    "default_popup": "pages/popup.html",
    "matches": [
      "https://twitter.com/*",
      "https://mobile.twitter.com/*"
    ],
    "default_icon": {
      "16": "icons/focussed_twitter_16.png",
      "32": "icons/focussed_twitter_32.png",
      "48": "icons/focussed_twitter_48.png",
      "128": "icons/focussed_twitter_128.png"
    }
  },
  "icons": {
    "16": "icons/focussed_twitter_16.png",
    "32": "icons/focussed_twitter_32.png",
    "48": "icons/focussed_twitter_48.png",
    "128": "icons/focussed_twitter_128.png"
  }
}