Examine source code of playbackRate.js

{
  "name": "playbackRate.js",
  "description": "Control video playback rate anywhere.",
  "version": "1.1",
  "manifest_version": 2,
  "permissions": [
    "activeTab"
  ],
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "run_at": "document_end",
      "js": [
        "playbackRate.js"
      ],
      "all_frames": true
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{239523ec-852c-46bb-a3ef-912a9c9f10bb}"
    }
  }
}