It's been a while since I updated this. I cleaned out the ancient stuff and added how to stop Thunderbird update check.
Type 'Run' in search and select 'Run' app
In 'Run' app type regedit and click on Ok
HKEY_LOCAL_MACHINE\Software\Policies
Create new subkey called 'Mozilla'
HKEY_LOCAL_MACHINE\Software\Policies\Mozilla
Then create new subkey called 'Thunderbird'
HKEY_LOCAL_MACHINE\Software\Policies\Mozilla\Thunderbird
On the right, create a new 32-Bit DWORD value DisableAppUpdate.
Note: Even if you are running 64-bit Windows you must still create a 32-bit DWORD value.
Set its value to 1.