Examine source code of ManaFlow

{
  "manifest_version": 2,
  "name": "ManaFlow",
  "version": "1.0.0",
  "author": "Lost Saint",
  "description": "Show FPS graph",
  "browser_action": {
    "default_icon": {
      "19": "assets/fps-19.png",
      "38": "assets/fps-38.png"
    },
    "default_title": "ManaFlow"
  },
  "icons": {
    "16": "assets/fps-dr-16.png",
    "48": "assets/fps-dr-48.png",
    "128": "assets/fps-dr-128.png"
  },
  "background": {
    "scripts": [
      "browser-polyfill.min.js",
      "background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "browser-polyfill.min.js",
        "main.js"
      ],
      "css": [
        "main.css"
      ]
    }
  ],
  "permissions": [
    "activeTab"
  ],
  "content_security_policy": "script-src 'self'; object-src 'self'",
  "browser_specific_settings": {
    "gecko": {
      "id": "{01e0b0c0-4ad8-44ae-b1c7-3976d6408590}"
    }
  }
}