Rated 4 out of 5 stars

Adkat, you need to do as the author says to do:

After installing the extension, find the new "close" button in the toolbar customization panel and drop it in your prefered place

So, click on your toolbar, go to 'customize' look for the Close n' Forget and drag and drop it where you want it.

This review is for a previous version of the add-on (0.6.2).