Good. Simple. On point. But I would dev to update and increase the visibility of the icon and font number size.

Ok, simple, can change the background color (but nothing else), sits near the URL bar.

If you need a Tab Counter that works post Firefox 57, this is the best one there is. Simple and no hassle.

Not sure if it is part of the limitation of new Firefox extension, all these numbers are Badges to the icon, instead of a Icon itself. Something that irritates me a little.