It's super great but I have an issue now on Linux Firefox 91. Duplicate Tabs requires Containers, that I deactivate. Containers, when activated for Duplicate Tabs, hinder my right-click, C keyboard shortcut to quickly copy URL of a link, which I need every 5 minutes. I had to deactivate this extension, sadly...

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.

Great plugin, but the permissions could be chosen more carefully.
I tried to run it without "webRequest", "webRequestBlocking", "" and it seems to work well.

(I looked into the code and found nothing fishy)