Examine source code of Page Ruler

{
  "version": "0.1.8",
  "name": "Page Ruler",
  "manifest_version": 3,
  "homepage_url": "https://mybrowseraddon.com/page-ruler.html",
  "description": "Measure page elements size in pixel with an easy-to-use ruler.",
  "commands": {
    "_execute_action": {}
  },
  "options_ui": {
    "open_in_tab": true,
    "page": "data/options/options.html"
  },
  "permissions": [
    "storage",
    "scripting",
    "activeTab"
  ],
  "browser_specific_settings": {
    "gecko": {
      "strict_min_version": "142.0",
      "id": "{23f77b40-cee8-40b4-910c-399170a36690}",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  },
  "background": {
    "scripts": [
      "lib/config.js",
      "lib/chrome.js",
      "lib/runtime.js",
      "lib/common.js"
    ]
  },
  "action": {
    "default_title": "Page Ruler",
    "default_icon": {
      "16": "data/icons/16.png",
      "32": "data/icons/32.png",
      "48": "data/icons/48.png",
      "64": "data/icons/64.png"
    }
  },
  "icons": {
    "16": "data/icons/16.png",
    "32": "data/icons/32.png",
    "48": "data/icons/48.png",
    "64": "data/icons/64.png",
    "128": "data/icons/128.png"
  }
}