It is possible to run two instances of Thunderbird at the same time, by specifying the command line option -no-remote. See Command Line Options for more information (Thunderbird has the same command line options as Firefox.)

Hi thanks for that - I am not technical but think I understand what to do but tried shift +F2 and it did not work the F2 key is volume reduction and that is all it does - using Windows 10 on a Lenovo YOGA 510

I don't see Shift+F2 in the command line options, but that doesn't work for tb. You have to start 2nd tb with command line options : thunderbird -no-remote -P

Misunderstanding - sorry in the instructions it says to open the comand line use Shift + F2 - see this :

Command line options are used to specify various startup options for Mozilla applications. For example, you can use command line configuration options to bypass the Profile Manager and open a specific profile (if you have multiple profiles). You can also control how Mozilla applications open, which components open initially, and what the components do when they open. This page describes the commonly used options and how to use them. You can open the Command Line Interface by pressing Shift + F2.

I am using Google Chrome will the Profile Switcher add-on work as I see it says you must be using Firefox