Exceptional extension, full of options. It can check the container of each tab, if wanted, so there's no risk of closing tabs with the same URL, but with different credentials. It can search for duplicates in different windows. It lists the duplicates in a pop-up dialogue, so individual tabs may be closed.

It has an option to compare titles, instead of URL, which is not so useful (instead, it could compare both URL plus title for a match, skipping some Pages which use cookies, local storage and other data bases to manage states, without relying on URL...)

Edit: I noticed that this extension has "fontawesome" inside, which only awesome thing about it is that it makes the installed extension almost 1 MB bigger that it should be! Would it be possible to remover that font in the next version? I don't know which glyphs are used by the extension, but, maybe, relying on the system's installed Unicode fonts would suffice?