Examine source code of Temp Mail

{
  "name": "Temp Mail - Disposable Temporary Email",
  "manifest_version": 2,
  "default_locale": "en",
  "homepage_url": "https://temp-mail.io",
  "icons": {
    "16": "./icons/icon-16.png",
    "48": "./icons/icon-48.png",
    "64": "./icons/icon-64.png",
    "128": "./icons/icon-128.png",
    "256": "./icons/icon-256.png",
    "512": "./icons/icon-512.png",
    "1024": "./icons/icon-1024.png"
  },
  "options_ui": {
    "page": "options.html",
    "open_in_tab": true
  },
  "background": {
    "scripts": [
      "./js/background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "http://*/*",
        "https://*/*"
      ],
      "exclude_matches": [
        "https://*.temp-mail.io/*"
      ],
      "js": [
        "js/content-script.js"
      ],
      "all_frames": true,
      "match_about_blank": true
    }
  ],
  "commands": {
    "_execute_action": {
      "suggested_key": {
        "windows": "Ctrl+Shift+E",
        "mac": "Command+Shift+E"
      }
    }
  },
  "permissions": [
    "storage",
    "tabs",
    "contextMenus",
    "notifications",
    "https://*.temp-mail.io/*",
    "https://www.google-analytics.com/*"
  ],
  "web_accessible_resources": [
    "css/*.css",
    "fonts/*.woff2",
    "*.png"
  ],
  "version": "2.1.3",
  "description": "Temp Mail allows you to easily keep your email address clean and safe from spam and hackers by providing you temporary email",
  "browser_specific_settings": {
    "gecko": {
      "id": "tempmail@temp-mail.io"
    }
  },
  "browser_action": {
    "default_icon": {
      "16": "./icons/icon-16.png",
      "20": "./icons/icon-20.png",
      "24": "./icons/icon-24.png",
      "32": "./icons/icon-32.png",
      "40": "./icons/icon-40.png"
    },
    "default_popup": "./popup.html",
    "default_title": "Temp Mail"
  }
}