Examine source code of Certainly Private

{
  "manifest_version": 2,
  "name": "Certainly Private",
  "version": "1.0.2resigned1",
  "description": "Hide your IP address like a VPN, only more convenient",
  "icons": {
    "48": "48-favicon.png",
    "72": "72-favicon.png",
    "96": "96-favicon.png"
  },
  "web_accessible_resources": [
    "48-favicon.png",
    "72-favicon.png",
    "96-favicon.png"
  ],
  "browser_action": {
    "default_icon": "48-favicon.png",
    "default_title": "Certainly Private Browsing"
  },
  "applications": {
    "gecko": {
      "id": "@tab-proxy",
      "strict_min_version": "57.0"
    }
  },
  "homepage_url": "https://github.com/gdestuynder/tab-proxy",
  "options_ui": {
    "page": "options.html"
  },
  "permissions": [
    "contextualIdentities",
    "cookies",
    "tabs",
    "activeTab",
    "sessions",
    "webRequest",
    "webRequestBlocking",
    "proxy",
    "storage",
    "<all_urls>"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  }
}