Examine source code of webtimer

{
  "name": "webtimer",
  "version": "0.1.0",
  "author": "jh2946",
  "manifest_version": 2,
  "description": "track how much time you spend on websites",
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "permissions": [
    "tabs",
    "storage",
    "unlimitedStorage"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "webtimer@jh2946"
    }
  },
  "browser_action": {
    "default_title": "webtimer",
    "default_popup": "popup.html"
  },
  "icons": {
    "48": "icon_48x48.png"
  }
}