Bugzilla

> Update from what?

From the last version before v115. The download from the official site and the update were performed manually. Automatic updates are disabled by policy.

> Thanks for those tests and details. A stronger test is start Windows in safe mode. 
> * Please start *Windows* in safe mode with networking enabled  https://support.microsoft.com/en-us/help/12376/windows-10-start-your-pc-in-safe-mode
> * Still in Windows safe mode, start Thunderbird in Troubleshoot mode  https://support.mozilla.org/en-US/kb/troubleshoot-mode-thunderbird
> 
> Does problem go away?

Thanks, but no, it doesn't. It still hangs. There is no change except for visuals (no greying in svga mode due to unresponsiveness).  As said, troubleshoot mode does not prevent it, it may delay it somewhat because there may be less background http traffic. There are no plugins active. No antivirus or anything else that would [hook](https://en.wikipedia.org/wiki/Hooking_) Thunderbird is active. The system has few third party background processes running.

> Without some smoking gun pointing conclusively to network I seriously doubt that is the cause.

Trigger or cause is unknown at this point, but it is a reasonable suspicion. The hang often occurs when a xhttp link opening window is shown as described. It is not immediate, it may take hours to a day.  Suggested method to reproduce in comment 6. Try this for a few days, not shutting a window popping up, and see it it doesn't cause hanging problems.

Perhaps an open protocol/application selection window blocks the next protocol/application window, which would possibly cause the program to hang? e.g. something blocking a thread that the main program is waiting for. Blocking I/O, threading or network requests are suspects when programs hang.