It doesn't work well recently. It needs to be fixed.

UPDATE (2026-06-28):
Awesome to see the developer is actively maintaining this add-on project and has implemented a lot of the features I requested all those years ago! Their response made me add this extension again, seeing as I have been running into the same 'too many tabs' problems as years ago.

Point 1: Appreciate that tip!
Point 2: The open popup on duplicate detected seems to be buggy on my setup, popping up randomly on pages that have been open, and not always loading on some other pages. Will have to skip using that for now.
Point 3: I think this point still stands, in practice, even though I see there is that option in theory. It's nice to know I can tell which of the tabs listed are new or old based on how they are displayed as compared to the setting I have in place, although I am not sure that is super intuitive to new users of the add-on. I wish there was a way to note the window each Tab is in, to be more informed with making dynamic decisions as we use the browser. Sometimes it makes sense to keep the newer tabs because they are more relevant when tied to the current tab stack we're browsing on. But sometimes it is more useful to keep the old instead of loading yet another duplicate tab, for instance when u open a duplicate in the same browsing session.

Either way the add-on feels much better than I remember it being 6 years ago, so I am upgrading my rating to the 5 stars it deserves.

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ORIGINAL (2020-11-26):
This Extension is nearly perfect! The best of the duplicate tab closing extensions on Firefox. I would love to see a couple features that I think would push this into the perfect 5* range.

[1] Whitelist should be available with the 'do nothing' option so that it applies to the "Close All" button as well, so that I can exclude certain pages (such as New Tab or about:blank) but still use that option.
[2] Add the option to pop up a Notification on duplicate. Automatically removing tabs has caused me issues, so I do not use that feature, but I still would love an option to know when I am duplicating an existing tab in the moment.
[3] In the duplicate tab notification window it would be nice to have the options to close New or Old duplicated tab, or to do nothing.

Thanks for all the hard work!

-Shrunk mode bug-
when all options are unpinned and then all options are hidden by shrunk mode, I can't unhide them again. when I click shrunk mode button, nothing is happens.

Does exactly what it says on the tin. Quite essential if you've got loads of tabs open and tend to open the same stuff...

works great!!. Additionally one thing i want is that it should detect duplicate tabs in same container but different windows. When scope is selected as "container" i am able to open duplicate tabs for a particular container across different firefox windows.
i can select scope as "all windows" but then I will not be able to open duplicate tabs in different containers.

Update: Thanks for implementing this

It has all of the options I need like keeping the newer tab open or eliminating the search part from the url. Thank you!

Works perfectly and very useful. Nicely set up, with important options easily accessed. Thank you dev!

1 question - can you have the Container and All windows options both selected? If so, a tick next to container option would be helpful.

A feature request-would be helpful if the dups list was colour-coded by container (or some other ID) and ability to select the tab in the correct container to keep (or maybe keep 2 selected tabs in 2 containers and delete the other 8 dups or in wrong containers!)

Outstanding for its ability to find duplicates across multiple windows.

Thanks Dev, for this add-on.
It has been doing a good job for months, but seems to be inactive since a few weeks.
My 5-star review stands anyway. Thank you again.

It works OK, but it is very slow. I'm a tab hoarder and the addon showed nearly 800 duplicate tabs when I first downloaded it. I thought it would be a simple matter of hitting the "Close all duplicate tabs" button to get rid of the tabs, but nope! That crashed Firefox. Not only that, but when I restarted not a single duplicate tab had been dealt with...so either the process removes them all or it just crashes and removes none of them. Great.

So then I started removing the duplicates one by one, which is a time consuming process considering the addon lags for a good 2-3 seconds when closing each tab. Even attempting to quickly move through the list by simply going down and rapidly clicking the x's doesn't speed it up...it's just slow. I finally just made a mouse macro that clicked through them for me using a program called Mouse Recorder Premium...for those without such a program this part would have sucked!

So I pared the list down to 500. As an experiment I wanted to see if the addon would handle 500. Nope. Crashed again, but this time it also decided to crash Firefox every single time I tried to restart it as well...great! I disabled the addon after a few crashes and FF was able to start again. When I re-enabled the addon it was clear not a single tab had been removed and I still had 500.

Finally, I ran my macro a bit more and got it down to 150 (I actually wanted to stop at 250 and see if it would handle that but I got distract and the macro had already ran it down to 150 when I check it again...oh well). Now here's the reason why I didn't just rate this thing 1 star. It actually dealt with the 150 tabs pretty easily. Click the button and POOF they're gone. So I would say for the average user this addon will work quite the treat, but if you're someone like me that has a massive duplicate tab problem, well, expect to put in some work clicking those little x's and waiting.