Okay. But when I snap the tab out of the window, the numbers on the remaining that is not updated

So nice add-on. I like this.
But it is not accessible some tab that opening https://addons.mozilla.org .
I suggest that to add add-on's description about this behavior.

Not working at this moment on last version.

Perfect, does what I want and what it says

.
-> Tab Numbers

Aurait pu m'être très utile - malheureusement, les no. ne se mettent pas à jour si on ferme un onglet et ,en plus, ils sont mémorisés dans les marque-pages... ce qui ne me convient pas.

Du coup, je l'ai désinstallé
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It is working. But do you mind to answer why you need Access your data for all websites permission? Might be an exploit. Careful guys

Probably works fine for simple cases, but gets confused when using the Simple Tab Groups add-on. Keeps counting past 9.

Very interesting! Thanks Sachin.