It is generally a good idea for each user on a computer to have their own 'User Account' as this means each users desktop can be only accessed by a password. This means Thunderbird runs within each User Account and creates a separate profile within each User Account offering a degree of privacy for documents including emails for each User Account.

If you create a 'Family' User Account (with or without password) so anyone can access that User Account as a general use account, Thunderbird will run and create a separate profile for any mail accounts (email addresses) you add. If more than one person has a mail account in that profile, then none of those emails or mail account details can be considered private.

This does mean your current User Account, which should have a password to access the desktop, with access to your emails can be kept more private.

Thank you, Toad-Hall, for your confirmation of my intentions. We are now two users on this computer, my e-mail program being Thunderbird and my wife's being an Internet-accessed alternative of her choosing. We work comfortably with one User Account. The "Family" User Account will be solely for our dealings with Microsoft now that we have been obliged to move from Office 2010 to Office 2020. When I bring down Office 2020 tomorrow under User Account Family I expect it will be interesting, in part because Microsoft might not find Office 2010 under User Account Family, unless I make a point of loading that discontinued software there beforehand. If you've any warnings for me, I'll welcome them, as I have your earlier response.