Every Other Email Opens In A New Tab

[jayhanig]

This is weird and just started happening a couple of days ago:

For years and years, I have preferred my emails to just show the preview panel. I have a fairly large monitor and I have enough space to usually show the entire message without opening either a new tab or a new window. What little I can't see I can just scroll down to see.

Suddenly, it now opens every other message in a new tab when I click on the message in the list. What's up with that? When I go to Tools > Options > Advanced > Display > Advanced > Reading, I have it set to open messages in an existing message window.

I also am suffering frequent freezes. What is going on?

Thunderbird 52.2.1 (32 bit)
Windows 10 Home v1607 (64 bit)
Avast Free Antivirus v17.5.2303
MalwareBytes Premium 3.12.1733

[DanRaisch]

Does the same thing occur if you launch the application in Mozilla Safe Mode? http://kb.mozillazine.org/Safe_mode