Rated 1 out of 5 stars

I read the installation instructions on your GitHub page to make sure I wasn't doing anything wrong (it's hard to screw up installing an extension) but in the Thunrderbird Menu Bar under Tools there's no extra options after installing the extension. Nothing changes whether it's installed or not. If I have an old version of Thunderbird and the old version of this extension the extra menu options are there under Tools, but all import options are grayed out.
I'm running Thunderbird 68.10.0 (latest) and I have tried installing the extension direction from the Add-Ons store, and from the XPI file from GitHub—same results, there's no added menu options in the Tools menu.
On your GitHub page under Brief Usage Instructions there's a part that says "You may have to enable the Menu Bar from Preferences to make it display", but there's no 'preferences' menu option that I can find in Thunderbird.

This review is for a previous version of the add-on (4.1.0). 

This really is a question not a review.
Have you looked at the help that describes the menu options?
import options appear when you right-click on a folder that allows imports. typically local folders