Examine source code of Discord Customizer

{
  "manifest_version": 2,
  "default_locale": "en",
  "name": "Discord Customizer",
  "description": "Discord Customizer by DAZZY#7373",
  "icons": {
    "128": "icon.png"
  },
  "version": "1.0.1",
  "author": "Dazzy",
  "minimum_chrome_version": "41",
  "permissions": [
    "storage"
  ],
  "browser_action": {
    "default_popup": "popup.html"
  },
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": false
  },
  "content_scripts": [
    {
      "matches": [
        "https://discord.com/*",
        "https://discord.com/channels/*",
        "https://ptb.discord.com/channels/*",
        "https://canary.discord.com/channels/*"
      ],
      "css": [
        "main.css"
      ],
      "js": [
        "discord.js"
      ],
      "run_at": "document_start"
    },
    {
      "matches": [
        "https://www.youtube.com/*"
      ],
      "js": [
        "youtube.js",
        "content_script.js"
      ],
      "run_at": "document_idle"
    },
    {
      "matches": [
        "https://soundcloud.com/*"
      ],
      "js": [
        "soundcloud.js",
        "content_script.js"
      ],
      "run_at": "document_idle"
    },
    {
      "matches": [
        "https://app.plex.tv/desktop"
      ],
      "js": [
        "plex.js",
        "content_script.js"
      ],
      "run_at": "document_idle"
    }
  ]
}