Examine source code of ytm

{
  "manifest_version": 2,
  "name": "ytm",
  "version": "1.1",
  "description": "Adds a video controller to the browser so that youtube videos can be controlled from any tab",
  "icons": {
    "48": "icons/music_video-24px.svg"
  },
  "permissions": [
    "activeTab",
    "<all_urls>",
    "tabs"
  ],
  "browser_action": {
    "default_icon": "icons/headphones.svg",
    "default_title": "Music Controller",
    "default_popup": "popup/index.html"
  }
}