Examine source code of Ruler Grid

{
  "manifest_version": 3,
  "name": "Ruler Grid",
  "description": "Measure and explore the web: rulers, eyedropper, fonts, code snippets, and more.",
  "version": "1.3.0",
  "icons": {
    "16": "icon/default/16.png",
    "32": "icon/default/32.png",
    "48": "icon/default/48.png",
    "96": "icon/default/96.png",
    "128": "icon/default/128.png"
  },
  "permissions": [
    "storage",
    "activeTab",
    "tabs",
    "contextMenus",
    "scripting",
    "declarativeNetRequest",
    "downloads"
  ],
  "host_permissions": [
    "<all_urls>"
  ],
  "action": {
    "default_title": "Ruler Grid — toggle the panel"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "ruler-grid@local-dev",
      "strict_min_version": "140.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  },
  "web_accessible_resources": [
    {
      "resources": [
        "pro-upsell/*.png"
      ],
      "matches": [
        "<all_urls>"
      ]
    }
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "options_ui": {
    "page": "options.html"
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "all_frames": false,
      "run_at": "document_idle",
      "js": [
        "content-scripts/overlay.js",
        "content-scripts/responsive-restore.js"
      ]
    }
  ]
}