Examine source code of ruler

{
  "name": "__MSG_appName__",
  "version": "2.0.4resigned1",
  "description": "__MSG_appDescription__",
  "author": "Ian Remmel",
  "default_locale": "en",
  "permissions": [
    "activeTab"
  ],
  "background": {
    "scripts": [
      "scripts/background.js"
    ],
    "persistent": false
  },
  "icons": {
    "16": "images/icon-16.png",
    "48": "images/icon-48.png"
  },
  "browser_action": {
    "default_icon": {
      "19": "images/icon-19.png",
      "38": "images/icon-38.png"
    },
    "default_title": "ruler"
  },
  "manifest_version": 2,
  "browser_specific_settings": {
    "gecko": {
      "id": "{b1355a29-9265-4b5e-a3ad-e9d61265d5ac}"
    }
  }
}