Examine source code of Sum Tabs

{
  "manifest_version": 2,
  "name": "Sum Tabs",
  "version": "1.1resigned1",
  "description": "Adds a button with the number of tabs to your toolbar",
  "icons": {
    "128": "icon/tab-counter-icon.svg"
  },
  "browser_action": {
    "default_icon": "icon/tab-counter-icon.svg",
    "default_popup": "popup/tab_counter.html"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "permissions": [
    "tabs"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{7d2b5a89-40aa-4f7c-b8c8-8013a3be8abe}"
    }
  }
}