Examine source code of Media Control

{
  "manifest_version": 2,
  "name": "Media Control",
  "description": "View and control all media that is playing in your browser.",
  "version": "0.1.4",
  "icons": {
    "16": "/icon/icon-16.png",
    "24": "/icon/icon-24.png",
    "48": "/icon/icon-48.png",
    "64": "/icon/icon-64.png",
    "96": "/icon/icon-96.png",
    "128": "/icon/icon-128.png",
    "256": "/icon/icon-256.png"
  },
  "homepage_url": "https://github.com/ungive/media-control-extension",
  "permissions": [
    "tabs",
    "storage",
    "webNavigation"
  ],
  "web_accessible_resources": [
    "inject.js"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "media-control-extension@jonasvandenberg.net",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  },
  "background": {
    "persistent": true,
    "scripts": [
      "background.js"
    ]
  },
  "browser_action": {
    "default_title": "Media Control",
    "default_popup": "popup.html"
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "all_frames": true,
      "run_at": "document_start",
      "js": [
        "content-scripts/inject.js"
      ],
      "world": "MAIN"
    },
    {
      "matches": [
        "<all_urls>"
      ],
      "all_frames": true,
      "run_at": "document_end",
      "js": [
        "content-scripts/media.js"
      ]
    }
  ]
}