Examine source code of SimplyFocus

{
  "manifest_version": 2,
  "name": "SimplyFocus",
  "version": "1.1",
  "description": "Block distracting sites to maintain focus",
  "permissions": [
    "storage",
    "webRequest",
    "webRequestBlocking",
    "<all_urls>"
  ],
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": {
      "48": "icon.png",
      "96": "icon.png"
    }
  },
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": true
  },
  "icons": {
    "48": "icon.png",
    "96": "icon.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{5c987c08-f927-45ef-9325-cc4b356b7db6}"
    }
  }
}