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.

It works well. It's placed properly and allows changing the background color.

basically just a counter, works well, and is put in a nice position. no more no less. 5 stars