Examine source code of TimeMail

{
  "manifest_version": 2,
  "name": "TimeMail",
  "version": "1.0",
  "description": "Schedule emails to be sent at specific times across various email services",
  "icons": {
    "48": "icons/icon-48.png",
    "96": "icons/icon-96.png"
  },
  "permissions": [
    "storage",
    "alarms",
    "notifications",
    "<all_urls>"
  ],
  "browser_action": {
    "default_icon": "icons/icon-48.png",
    "default_title": "TimeMail",
    "default_popup": "popup/popup.html"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "*://mail.google.com/*",
        "*://outlook.live.com/*",
        "*://outlook.office365.com/*",
        "*://mail.yahoo.com/*"
      ],
      "js": [
        "content_scripts/email_injector.js"
      ]
    }
  ],
  "options_ui": {
    "page": "options/options.html",
    "open_in_tab": true
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{6eb1b4c3-1f8e-49c9-a87b-d912318daa81}"
    }
  }
}