A lightweight, efficient, and permission-free extension for Mozilla Thunderbird that minimizes the main Thunderbird window immediately after startup.

Installation
Option 1 - From addons.thunderbird.net (ATN)

https://addons.thunderbird.net/en-US/thunderbird/addon/havoc-startup-minimizer

Option 2 - Install Manually

1. Download the latest .xpi file.
2. In Thunderbird, open: Tools → Add-ons and Themes → Extensions
3. Click the gear icon → Install Add-on From File...
4. Select the downloaded .xpi file.