Examine source code of Tab Numbering

{
  "name": "Tab Numbering",
  "description": "This extension writes the tab number to the first eight tabs, the ones accessible with ctrl/cmd + number",
  "version": "0.1.2resigned1",
  "permissions": [
    "tabs",
    "http://*/*",
    "https://*/*"
  ],
  "icons": {
    "128": "tab-numbering.png"
  },
  "manifest_version": 2,
  "background": {
    "scripts": [
      "tab-numbering.js"
    ]
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{5ec3a50c-9307-4f1e-a47d-0e86db5cc8a3}"
    }
  }
}