Examine source code of Tab Focus Timer

{
  "manifest_version": 2,
  "name": "Tab Focus Timer",
  "short_name": "Tab Timer",
  "author": "Santiago Frega",
  "version": "1.3.2",
  "description": "Track how long you spend on each website with daily browsing statistics.",
  "icons": {
    "48": "icon.png"
  },
  "permissions": [
    "tabs",
    "webNavigation",
    "storage",
    "<all_urls>"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": "icon.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{fa2ec278-c128-43dc-a962-eedaaa68b2d1}"
    }
  }
}