Examine source code of GHtmlMail

{
  "description": "Redirects calls to the GMail inbox page to the HTML version.",
  "manifest_version": 2,
  "name": "GHtmlMail",
  "version": "1.0",
  "homepage_url": "https://github.com/kleiba/ghtmlmail",
  "icons": {
    "48": "ghtmlmail-icon-48.png"
  },
  "permissions": [
    "webRequest",
    "webRequestBlocking",
    "*://mail.google.com/mail/*"
  ],
  "background": {
    "scripts": [
      "ghtmlmail.js"
    ]
  },
  "browser_specific_settings": {
    "gecko": {
      "strict_min_version": "57.0a1"
    }
  }
}