update: The issue with addon closing non-duplicates seems to be resolved.
Working as intended now.

I also noticed a weird interaction between notifications. Seems like first notification received will cancel all the others when it expires. So for example, if second and any subsequent notifications are shown just before first one expires, they will all be closed almost instantly.

Thanks! It's got useful options

So good idea:
Like Chrome do!
But seems not working with Waterfox Classic ?

It is very useful because it closes duplicate tabs only when clicking on a link, and does not close duplicate tabs when using 'Duplicate Tab' tab menu or bookmark.