Examine source code of GUI Injector

{
  "manifest_version": 2,
  "name": "GUI Injector",
  "version": "1.0",
  "description": "Inject GUI script into specific websites",
  "permissions": [
    "activeTab",
    "*://*.blooket.com/*"
  ],
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": false
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.blooket.com/*"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_end"
    }
  ],
  "browser_action": {
    "default_popup": "popup.html",
    "default_title": "GUI Injector",
    "default_icon": "icon.png"
  },
  "icons": {
    "16": "icon.png",
    "32": "icon.png",
    "48": "icon.png",
    "96": "icon.png"
  },
  "web_accessible_resources": [
    "gui.js"
  ],
  "applications": {
    "gecko": {
      "id": "gui-injector@extension.local",
      "strict_min_version": "58.0"
    }
  }
}