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
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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).