manifest.json

{

  "description": "Adds a select all e-mails button to old Gmail interface. See https://github.com/mmendescortes/select-all-emails-on-old-gmail-interface",
  "manifest_version": 2,
  "name": "Select all e-mails on old Gmail interface",
  "version": "1.1",
  "homepage_url": "https://github.com/mmendescortes/select-all-emails-on-old-gmail-interface",
  "icons": {
    "48": "icons/icon.png"
  },

  "content_scripts": [
    {
      "matches": ["https://mail.google.com/mail/*/h*"],
      "js": ["extension.js"]
    }
  ]

}