Use separate Windows user accounts for the other users and set a password for your own Windows account to make it impossible for other to open files in your ccount.

In a Windows OS .... Control Panel > User Accounts

Create a User Account for yourself and set it up as Administrator. Create a password for yourself.

Create other User Accounts for other people or create a 'Guest' user account which anyone can use, without any password.

Make sure to 'create a password reset disk'. This option is available in Control Panel > User Accounts. This is not obligatory, but I would advise you to create one just in case you forget the password.

Your Thunderbird Profile folder containing all your emails etc will be stored within the User Account. Only access to the User Account will allow access to reading the emails.