Examine source code of PMMG Extended

{
  "manifest_version": 2,
  "name": "PMMG Extended",
  "description": "Improve and tweak the interface elements of PrUn website",
  "version": "1.13.4",
  "icons": {
    "128": "icon128.png"
  },
  "browser_action": {
    "default_popup": "popup.html"
  },
  "permissions": [
    "https://apex.prosperousuniverse.com/",
    "https://script.google.com/",
    "https://script.googleusercontent.com/",
    "https://rest.fnar.net/",
    "storage",
    "activeTab",
    "scripting",
    "tabs",
    "webNavigation"
  ],
  "content_scripts": [
    {
      "matches": [
        "https://apex.prosperousuniverse.com/*"
      ],
      "js": [
        "document_start.js"
      ],
      "run_at": "document_start"
    },
    {
      "matches": [
        "https://apex.prosperousuniverse.com/*"
      ],
      "js": [
        "main.js"
      ],
      "css": [
        "css/pmmg-style.css"
      ],
      "run_at": "document_end"
    }
  ],
  "background": {
    "scripts": [
      "background_script_mv2.js"
    ]
  },
  "web_accessible_resources": [
    "css/*.css",
    "*.js.map"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{28d62d88-823e-4327-9d7c-cb621d63bb7d}"
    }
  }
}