Examine source code of Days Without Overflow

{
  "manifest_version": 2,
  "name": "Days Without Overflow",
  "version": "1.0.1",
  "description": "Counts how many days have you survived without StackOverflow.",
  "browser_action": {
    "default_icon": {
      "64": "img/stack_overflow_icon.png"
    },
    "default_title": "Days Without Overflow",
    "default_popup": "html/popup.html",
    "browser_style": true
  },
  "permissions": [
    "history"
  ]
}