Examine source code of Gmail Label Organizer

{
  "manifest_version": 2,
  "name": "Gmail Label Organizer",
  "version": "2.1resigned1",
  "description": "Allows users to reorganize the Gmail system labels, i.e. to put the 'Important' label above 'Inbox'.",
  "applications": {
    "gecko": {
      "id": "{b7553286-a309-4899-b5ed-97c005ab703b}",
      "strict_min_version": "57.0a1"
    }
  },
  "browser_action": {
    "default_title": "Gmail Label Organizer",
    "browser_style": true,
    "default_icon": {
      "16": "icons/gmail.png"
    },
    "default_popup": "popup.html"
  },
  "permissions": [
    "activeTab",
    "storage"
  ],
  "icons": {
    "48": "icons/gmail.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://mail.google.com/*"
      ],
      "js": [
        "organizer.js"
      ]
    }
  ]
}