https://www.linuxuprising.com/2020/11/systray-x-is-thunderbird-68-tray-icon.html
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SysTray-X Is A Thunderbird 68+ Tray Icon With Unread Email Counter And Close / Minimize To Tray
SysTray-X is a Qt5 system tray icon for Thunderbird email client version 68 and newer, which shows the number of unread emails, and can minimize / clo