INTRO:
Lately a friend asked me to help with Thunderbird program under Windows that started to behave very badly.
After doing a normal de-installation and installing the very latest version, the same bad behavior remained.
It seemed that some corruption of Thunderbird working data had occurred, therefore it was then time to proceed to a full cleanup of Thunderbird as if it was never installed in this computer.

Here are the steps I did to do just that:

1) Make sure Thunderbird is stopped completely.

2) Press the following keys combination: Windows-R

3) I the field that popped up, Enter the command ‘cmd‘, this will start a terminal where we will issue some commands to do the clean-up.

4) In the following commands below make sure you replace the [YourUsername] with the username you used when logging into Windows. This is very Important!!! to have the right username in the commands below before issuing them.
Enter the following commands:
rmdir /s \Users\[YourUsername]\AppData\Local\Thunderbird
rmdir /s \Users\[YourUsername]\AppData\Roaming\Thunderbird

5) Enter the following command to start the editing of the registery.
regedit
BE VERY CAREFUL HERE !! Really make sure you don’t do anything else than the actions indicated below:

6) Navigate to: HKEY_CURRENT_USER\Software\Mozilla\Thunderbird
Delete this entire key (using the right mouse key menu)

Navigate to: HKEY_LOCAL_MACHINE\SOFTWARE\Mozilla\Thunderbird
Delete this entire key (if it exists)

7) Exit Regedit program

8) Back in the terminal issue the following command:
rmdir /s \Program Files\Mozilla Thunderbird

9) If you want to install a fresh Thunderbird, just download it from internet and install it.
It should install as if it never was installed in this computer. Then proceed to configure your email accounts.

Enjoy a new fresh Thunderbird