Examine source code of twitter-alt

{
  "manifest_version": 2,
  "name": "twitter-alt",
  "description": "Discover twitter image alternative text on hover/focus",
  "version": "0.0.1",
  "icons": {
    "64": "icons/icon-on.svg",
    "96": "icons/icon-on.svg",
    "128": "icons/icon-on.svg"
  },
  "background": {
    "scripts": [
      "background_script.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "*://twitter.com/*"
      ],
      "js": [
        "content_script.js"
      ],
      "css": [
        "content_style.css"
      ]
    }
  ],
  "page_action": {
    "default_icon": {
      "64": "icons/icon-on.svg",
      "96": "icons/icon-on.svg",
      "128": "icons/icon-on.svg"
    },
    "default_title": "twitter-alt",
    "show_matches": [
      "*://twitter.com/*"
    ]
  },
  "permissions": [
    "activeTab",
    "tabs",
    "storage"
  ]
}