Examine source code of speedSlider4Youtube

{
  "manifest_version": 2,
  "name": "YouTube Speed Control Extension",
  "version": "2.0",
  "description": "Control YouTube playback speed with a slider",
  "optional_permissions": [
    "activeTab"
  ],
  "icons": {
    "48": "icon.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://www.youtube.com/*"
      ],
      "js": [
        "content.js"
      ]
    }
  ],
  "browser_action": {
    "default_icon": {
      "48": "icon.png"
    },
    "default_title": "YouTube Speed Control Extension",
    "default_popup": "popup.html"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{f4f35e98-e1ea-4a9c-ac23-4b50613881f0}"
    }
  }
}