Examine source code of Desktiming

{
  "description": "Shows desktime's remaining time when clicking the desktime button on  browser toolbar.",
  "manifest_version": 2,
  "author": "Shajan Jacob",
  "name": "Desktiming",
  "version": "1.7resigned1",
  "homepage_url": "https://github.com/shajanjp/desktiming",
  "icons": {
    "64": "icons/clock.png"
  },
  "permissions": [
    "webRequest",
    "storage"
  ],
  "browser_action": {
    "default_icon": "icons/clock.png",
    "theme_icons": [
      {
        "light": "icons/clock.png",
        "dark": "icons/clock.png",
        "size": 64
      }
    ],
    "default_title": "Desktiming",
    "default_popup": "popup/desktime.html"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{2d3f03be-f82c-43ec-aa3b-b02a3fda959f}"
    }
  }
}