Examine source code of Quick Play

{
  "manifest_version": 2,
  "name": "Quick Play",
  "description": "Instantly increase playback speed with a single click.",
  "version": "1.2",
  "icons": {
    "48": "icons/icon48.png",
    "96": "icons/icon96.png"
  },
  "permissions": [
    "activeTab",
    "storage",
    "<all_urls>"
  ],
  "browser_action": {
    "default_popup": "popup.html"
  },
  "commands": {
    "speed-up": {
      "suggested_key": {
        "default": "Ctrl+Up",
        "mac": "Command+Up"
      },
      "description": "Increase Playback Speed +0.25x"
    },
    "speed-down": {
      "suggested_key": {
        "default": "Ctrl+Down",
        "mac": "Command+Down"
      },
      "description": "Decrease Playback Speed -0.25x"
    }
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "inject.js"
      ],
      "run_at": "document_idle",
      "all_frames": true,
      "match_about_blank": true
    }
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "web_accessible_resources": [
    "inject.js"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{cec52971-c5f1-4533-b768-750e81d49cd9}"
    }
  }
}