I tried a duplicate tabs extension that was way simpler than this that I liked at first. It could close duplicate tabs automatically in the background without interruptions, but it stopped working at some point. I tried this one next and it seems to be very robust. I wasn't sure that I needed all the bells and whistles at first but they have turned out to be quite useful after all, such as the URL format filters and the whitelist.

If I could add a suggestion, it would be super helpful to be able to whitelist a new tab. Not sure if this is possible. I tried entering a pair of empty double quotes into the whitelist field "" to see if that would work since I noticed that wildcards are also supported. Kind of a hackerly solution but I took a swing at it. Still closes them though. 😛

Recently the about:blank whitelist fails.

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.

The problem is that there are cases when all duplicate tabs are closed without keeping neither of them.
-auto-close on
-no filters
-keep newer tab (keep tab with HTTPS, keep pinned tab)
-scope: active window

The situation occurs when both tabs were loading simultaneous!

muß ich erst ausprobieren !

This is really handy and has a good set of options for fitting into whatever way you like to browse. You should absolutely give this a try, and open the options panel if it doesn't suit you out-of-the-box.

The one extra thing I'd like to see is an option to have settings like "ignore path" apply to particular domains only -- I'd love to be able to open four articles from the same website but reliably collapse four instances of the same web-app.

Super extension overall, but there is a bug in the settings handling for filters.
If "Ignore search part..." is set, then "Ignore hash part ..." isn't doing anything. Similarly of "Ignore path part ..." is set then the two other settings are useless.

This is due to "else if" being used in areMatchingURL function from urlUtils.js (line 24, 28). Switching this to independent ifs allows to respect all settings (and support urls having both hash and search signs.

If possible please bring a fix for this one (I can provide a pull request if the code is on some git repo).
Thanks in advance.

since Fire Quantum, no longer shows mini-window indicating duplicate tabs.

Shows the wrong number of duplicates.
More than really, even if real quantity of duplicates = 0
Perhaps it's conflict with "Tree Style Tab" or "BarTab Plus".
my FF version - 55.0.3 (x64)

UPD

https://addons.mozilla.org/firefox/addon/tree-style-tab/versions/?page=1#version-0.19.2017090601

https://addons.mozilla.org/firefox/addon/bartab-plus/

OK. I found how the conflict appears - when I use the "Unload" option of "BarTab Plus". "Duplicate Tabs Closer" defines the unloaded tabs as duplicates for some reason.