manifest.json

{

  "description": "Adds a browser action icon to the toolbar that allow to dispaly an horizontal ruler for web development purposes",
  "manifest_version": 2,
  "name": "DevRuler",
  "version": "1.0.2",
  // "homepage_url": "",
  "author": "Vince Damiani",
  "icons": {
    "48": "icons/ruler-48.png"
  },

  "permissions": [
    "<all_urls>", //very important, insertCss would not work without it
    "activeTab",
    "browsingData",
    "notifications",
    "storage",
    "tabs"
  ],

  "browser_action": {
    "default_icon": "icons/ruler-32.png",
    "theme_icons": [{
        "light": "icons/ruler-light-32.png",
        "dark": "icons/ruler-32.png",
        "size": 32
    }],
    "default_title": "DevRuler",
    "default_popup": "popup/ruler_popup.html"
  },

  "page_action": {
    "browser_style": true
  },

  // "content_scripts": [
  //   {
  //     // "matches": ["http://*.nytimes.com/*"],
  //     // "css": ["myStyles.css"],
  //     "matches": [
  //       "<all_urls>"
  //     ],
  //     "js": ["js/onload.js"]
  //   }
  // ],

  "options_ui": {
    "page": "options/options.html"
  },

  "browser_specific_settings": {
    "gecko": {
      "id": "devruler@developer.mozilla.org"
    }
  },

  // "applications": {
  //   "gecko": {
  //     "id": "devruler@example.com"
  //   }
  // },

  "background": {
    "scripts": [
      "onupdate.js"
    ]
  }
}