Examine source code of Popup Player for Spotify™

{
  "manifest_version": 2,
  "version": "0.1.2resigned1",
  "name": "Popup Player for Spotify™",
  "description": "Control Spotify web player from a toolbar popup (includes play, pause, skip previous and next tracks)",
  "permissions": [
    "*://open.spotify.com/*",
    "storage"
  ],
  "icons": {
    "16": "data/icons/16.png",
    "18": "data/icons/18.png",
    "19": "data/icons/19.png",
    "32": "data/icons/32.png",
    "36": "data/icons/36.png",
    "38": "data/icons/38.png",
    "48": "data/icons/48.png",
    "64": "data/icons/64.png",
    "128": "data/icons/128.png",
    "256": "data/icons/256.png"
  },
  "homepage_url": "http://add0n.com/player-for-spotify.html",
  "browser_action": {
    "default_icon": {
      "16": "data/icons/16.png",
      "18": "data/icons/18.png",
      "19": "data/icons/19.png",
      "32": "data/icons/32.png",
      "36": "data/icons/36.png",
      "38": "data/icons/38.png",
      "48": "data/icons/48.png"
    },
    "default_popup": "data/popup/index.html"
  },
  "background": {
    "persistent": false,
    "scripts": [
      "background.js"
    ]
  },
  "content_scripts": [
    {
      "run_at": "document_start",
      "matches": [
        "*://open.spotify.com/*"
      ],
      "js": [
        "data/inject.js"
      ]
    }
  ],
  "applications": {
    "gecko": {
      "id": "{b3c23112-f8d6-4d5a-a6f8-041f63778488}",
      "strict_min_version": "52.0"
    }
  }
}