Hi, Knowing this is the "ask the community" 's Thread, but don't know where else has official place to share about Thunderbird's info. For those who wonder how to change this settings (View message in new window), I had searched up and down the net there is no new updated method has been shared. It is easy and here is settings to change: Click at upper right corner resembles "Hamburger" icon > Settings > General > Scroll down till "Open messages in:" > Select "A new message window". Done. You're welcome :)