Examine source code of Measure Everything

{
  "manifest_version": 2,
  "name": "Measure Everything",
  "description": "Element distance measurement tool.",
  "version": "1.0.4",
  "author": "Marat Dulin",
  "license": "MIT",
  "browser_action": {
    "default_title": "Measure Everything",
    "default_icon": "icon16.png"
  },
  "background": {
    "scripts": [
      "js/background.js"
    ],
    "persistent": false
  },
  "commands": {
    "toggle-measure-everything": {
      "suggested_key": {
        "default": "Alt+Shift+M",
        "mac": "Alt+Shift+M"
      },
      "description": "Toggles Measure Everything"
    }
  },
  "icons": {
    "16": "icon16.png",
    "48": "icon48.png",
    "128": "icon128.png"
  },
  "permissions": [
    "activeTab"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{e1d11714-1c10-4d0c-b440-76336f4408be}"
    }
  }
}