Option A. Please update to 38.2.0

Option B. If option A did not help, please start *Windows'* safe mode with networking enabled - win8 http://windows.microsoft.com/en-us/windows-8/windows-startup-settings-safe-mode - win7 http://windows.microsoft.com/en-us/windows/start-computer-safe-mode#start-computer-safe-mode=windows-7 - XP http://www.microsoft.com/resources/documentation/windows/xp/all/proddocs/en-us/boot_failsafe.mspx

Still In Windows safe mode, start Thunderbird in safe mode - http://support.mozillamessaging.com/en-US/kb/safe-mode

Does the problem go away?

I updated to 38.2.0, same problem.

I apologize for not being as clear enough. Once I restart my computer, Mozilla runs just fine. It locks up my computer *only* immediately after it downloads emails for a second email account. So I'm not sure what I should do after I go into Safe Mode. Please elaborate.

After starting Windows in safe mode start Thunderbird in safe mode and do what you always do.

Christ1, thank you for taking the time to reply and to help solve my problem. However, I remain confused by your answer. It sounds to me like you're saying that I should run thunderbird in Safe Mode from now on. WIth respect, restarting in Safe Mode just to check my email simply makes no sense. I hope that's not what you actually meant. Will you be more specific on how going into Safe Mode is supposed to identify the cause of the problem I described?

Safe mode is primarily to determine whether your anti-virus software is causing any issues. Anti-virus software is not running in Windows safe mode.

Christ1, since you're concerned with AV, then the better test is to disable AV and check Tbird. So that's what I did. And Tbird worked. Re-enable AV. Re-test Tbird. Still works. Restart computer. Re-test Tbird. Still works.

In other words, the problem I described above is gone, but I have no idea why, which leaves me with very mixed feelings.

Thank you again for your time.