Examine source code of YouSpeed

{
  "manifest_version": 2,
  "name": "YouSpeed",
  "version": "1.1resigned1",
  "description": "Adds a playback speed slider for youtube.com",
  "icons": {
    "48": "i-48.png"
  },
  "applications": {
    "gecko": {
      "id": "youSpeedV2.1@selfSignedExt.org",
      "strict_min_version": "45.0"
    }
  },
  "permissions": [
    "activeTab"
  ],
  "content_scripts": [
    {
      "matches": [
        "*://*.youtube.com/*"
      ],
      "js": []
    }
  ],
  "browser_action": {
    "default_icon": {
      "19": "i-19.png",
      "38": "i-38.png"
    },
    "default_title": "youspeed",
    "default_popup": "choose_speed.html"
  }
}