Examine source code of CustomFireTab

{
  "manifest_version": 2,
  "name": "Custom FireTab URL",
  "version": "1.4.0",
  "description": "Set custom URLs for new tabs. Manage multiple URLs and choose your active homepage.",
  "author": "BigStrib",
  "icons": {
    "48": "icons/icon-48.png",
    "96": "icons/icon-96.png",
    "128": "icons/icon-128.png"
  },
  "permissions": [
    "storage",
    "tabs",
    "webNavigation"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": "icons/icon-48.png"
  },
  "chrome_url_overrides": {
    "newtab": "newtab.html"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "BCS6131990@blake.com",
      "strict_min_version": "79.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  }
}