FortiConverter 5.5 Python - Installation issue "Internet Explorer" Default Browser

Fortinets configuration migration tool FortiConverter (documentation) has been rewritten using python and has been launched in the past few months. In some special circumstances the installation could show the following error: "FortiConverter can not support Internet Explorer, please use Chrome or Firefox and set them as default browser.":
 

Problem:

You've changed the default browser of your Windows operating system to Chrome or Firefox - but the error still occurs during the installation.

Cause:

Your current Windows user is using Chrome or Firefox as default browser, but the administrator user, which is used to install FortiConverter, has still set Internet Explorer as default Browser.

Solution: 

Login to Windows with your administrator user, change the Windows Default Browser to Firefox or Chrome. Login again with your normal user, install FortiConverter without any issue.