I could not send emails with TB 45.0.0 so I went back to TB 38.6.0 Now to answer your question No. 1:
- When you install your favourite version, uncheck the Maintenance/update box in Advanced Install.
- After the install, go to the (X86) Program Files where you will find TB. Open its Folder and delete
maintenanceservice.exe
andmaintenanceservice_installer.exe
- Do NOT open the 'About Thunderbird' as it puts TB into an Update mode!