Examine source code of Checker Plus for Gmail™

{
  "browser_specific_settings": {
    "gecko": {
      "id": "checkerplusforgmail@jasonsavard.com"
    }
  },
  "name": "Checker Plus for Gmail",
  "description": "__MSG_description__",
  "version": "36.0",
  "homepage_url": "https://jasonsavard.com?ref=homepage_url&ext=gmail",
  "background": {
    "scripts": [
      "lib/Autolinker.js",
      "js/common.js",
      "js/checkerPlusForGmail.js",
      "js/mime/addressparser.js",
      "js/mime/buffer.js",
      "js/mime/iconv.js",
      "js/mime/encoding.js",
      "js/mime/mimelib.js",
      "js/account.js",
      "js/mail.js",
      "js/sanitizer/html4.js",
      "js/sanitizer/uri.js",
      "js/sanitizer/sanitizer.js",
      "js/off_screen.js",
      "js/background.js"
    ]
  },
  "action": {
    "default_icon": {
      "19": "/images/browserButtons/default/not_logged_in.png",
      "38": "/images/browserButtons/default/not_logged_in_retina.png"
    },
    "default_title": "Checker Plus for Gmail™",
    "default_popup": "popup.html?source=toolbar&setVia=manifest"
  },
  "icons": {
    "16": "/images/icons/icon_16.png",
    "32": "/images/icons/icon_32.png",
    "48": "/images/icons/icon_48.png",
    "64": "/images/icons/icon_64.png",
    "128": "/images/icons/icon_128.png"
  },
  "options_ui": {
    "page": "options.html",
    "open_in_tab": true
  },
  "commands": {
    "activateExtension": {
      "description": "__MSG_activateExtension__"
    },
    "compose": {
      "description": "__MSG_compose__"
    },
    "quickComposeEmail": {
      "description": "__MSG_quickComposeEmail__"
    },
    "refresh": {
      "description": "__MSG_refresh__"
    },
    "markAsReadInNotificationWindow": {
      "description": "__MSG_markAsReadInNotificationWindow__"
    },
    "markAllAsRead": {
      "description": "__MSG_markAllAsRead__"
    },
    "openEmailDisplayedInNotificationWindow": {
      "description": "__MSG_openEmailDisplayedInNotificationWindow__"
    },
    "dnd": {
      "description": "__MSG_doNotDisturb__"
    }
  },
  "content_scripts": [
    {
      "all_frames": true,
      "js": [
        "js/tabletView.js"
      ],
      "matches": [
        "https://mail.google.com/mail/mu/mp/*"
      ],
      "include_globs": [
        "https://mail.google.com/mail/mu/*mui=checkerPlusForGmail*"
      ],
      "run_at": "document_start"
    }
  ],
  "default_locale": "en",
  "permissions": [
    "alarms",
    "activeTab",
    "tabs",
    "idle",
    "notifications",
    "storage",
    "contextMenus",
    "identity",
    "cookies",
    "declarativeNetRequestWithHostAccess",
    "scripting"
  ],
  "optional_permissions": [
    "webRequest"
  ],
  "host_permissions": [
    "https://mail.google.com/"
  ],
  "optional_host_permissions": [
    "https://*.googleusercontent.com/"
  ],
  "manifest_version": 3,
  "web_accessible_resources": [
    {
      "resources": [
        "options.html",
        "contribute.html"
      ],
      "matches": [
        "https://*.jasonsavard.com/*",
        "https://checkout.stripe.com/*",
        "https://www.paypal.com/*",
        "https://commerce.coinbase.com/*"
      ]
    },
    {
      "resources": [
        "css/tabletView.css"
      ],
      "matches": [
        "https://mail.google.com/*"
      ]
    }
  ]
}