Examine source code of Screen Ruler

{
  "manifest_version": 2,
  "name": "Extension",
  "description": "",
  "version": "5.0.1",
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": true
  },
  "browser_action": {
    "default_icon": {
      "32": "icons/icon.png"
    }
  },
  "permissions": [
    "clipboardRead",
    "storage",
    "tabs"
  ],
  "icons": {
    "32": "icons/icon.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "data_collection_permissions": {
        "required": [
          "none"
        ],
        "optional": [
          "technicalAndInteraction"
        ]
      },
      "id": "{220eb399-db43-4b4d-a3e2-92cb2349684d}"
    }
  }
}