the good: you can customize color and it has options for resizing. Overall it was pretty decent although still not quite what I was looking for. Definitely like that it *has* preferences and being 'experimental' I wasn't sure what to expect coming in.

the bad: the resizing options didn't work for me at all.

the ugly: it had multiple different tab counts (current/open/hidden). I wanted to just have a plain 'all open tabs count' as the *only* number displayed but I was only able to turn off the 'hidden' tabs count in the settings. Due to this and the resizing not working correctly for me, this would display as "abc / xyz" with the 'a' and 'z' positions getting cut off when I had a large number of tabs open. Since I couldn't fix the sizing and I couldn't change it to only show *one* number, unfortunately I must move on.

Best of luck.

For those interested in similar criteria, so far Tab Count Icon by lllusion3418 has most of what I was looking for above but I have issues resizing in that one too.. maybe it is a limitation of WebExtensions / Linux / the combination?

Edit: FF v89.0.2 on Fedora 33 Cinnamon

Simple!
Maybe it should detect if we are in dark mode and display the count in white.

EDIT: Good improvement on the customization, numbers are still a bit little (the size of the icon don't get bigger, maybe put one number on top of the other number?), but over all it's an excellent extension.

The current tab index is a must over all other tab counters addons as it is very nice to know where we are in the middle of all those tabs

I'am using Firefox 70 on Ubuntu-MATE

Thanks Jonathon