Examine source code of Gmail Mod

{
  "name": "Gmail Mod",
  "short_name": "gmail-mod",
  "version": "2022.0.1",
  "description": "Adds an embedded audio and video player to Gmail for playing audio and video attachments.",
  "content_scripts": [
    {
      "matches": [
        "https://mail.google.com/*"
      ],
      "run_at": "document_start",
      "js": [
        "gmail-mod.js"
      ],
      "css": [
        "css/GmailMod.css"
      ]
    }
  ],
  "background": {
    "scripts": [
      "./background.js"
    ]
  },
  "icons": {
    "16": "images/icon16.png",
    "48": "images/icon48.png",
    "128": "images/icon128.png"
  },
  "options_ui": {
    "page": "html/options.html",
    "open_in_tab": false
  },
  "permissions": [
    "storage",
    "*://mail-attachment.googleusercontent.com/*",
    "https://mail.google.com/*",
    "http://mail.google.com/*",
    "*://mail.google.com/*",
    "*://*.google.com/*",
    "*://*.googleusercontent.com/*"
  ],
  "optional_permissions": [],
  "manifest_version": 2,
  "browser_specific_settings": {
    "gecko": {
      "id": "{f670f216-9980-42b1-84a3-4c511c27dc3a}",
      "strict_min_version": "57.0"
    }
  },
  "incognito": "spanning"
}