Problem started right afer I upgraded. I have been running Thunderbird 115.3.1 (32 bit) since its release in July. Ran great, really like this long over due upgrade toThunderbird. Today, Oct 18 I upgraded to Thunderbird 115.3.3 and now can no longer view any mail and can't open any folder that contains mail. Old or new, doesn't make a difference. Interaction with Thunderbird seems to depend on whether the folder contains mail or has a sub (child) folder that contains mail. The results of double clicking any folder that has mail depends if that folder has more than 1 subfolder. 1) If the folder has no child folders double clicking has no effect. Nothing happens. I can right click and select the folder but get no options. 2) If a folder does have multiple child folders, double clicking will open the parent folder and display the child folders. But none of the child folders will open. I'm running Windows Server 2008 R2 (64 bit) 2 x Intel Xeon E5-2690 3.2Ghz processors, 196GB RAM, 3 x 3TB hard drives.