Examine source code of calm

{
  "manifest_version": 2,
  "name": "calm",
  "version": "1.0",
  "description": "less tabs",
  "permissions": [
    "<all_urls>",
    "tabs"
  ],
  "applications": {
    "gecko": {
      "id": "calm@yourbrowser.com"
    }
  },
  "icons": {
    "48": "icon/icon_48.png",
    "96": "icon/icon_96.png"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_action": {
    "default_icon": {
      "48": "icon/icon_48.png",
      "96": "icon/icon_96.png"
    },
    "default_title": "Close Tabs"
  }
}