Examine source code of Yet Another Tab Counter

{
  "manifest_version": 2,
  "name": "Yet Another Tab Counter",
  "author": "Daniel Hofstetter (@dhofstet)",
  "version": "1.0.3resigned1",
  "description": "Shows the number of open tabs",
  "icons": {
    "48": "icons/tabcounter.svg"
  },
  "browser_action": {
    "browser_style": true,
    "default_icon": {
      "16": "icons/empty.svg"
    }
  },
  "background": {
    "scripts": [
      "tabcounter.js"
    ]
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{f004c841-12fa-4f3f-8b26-fc33813094d1}"
    }
  }
}