It works, but cannot display 4 numbers in cases you have more than 1000 tabs, 4th number is cut off

Wish I could adjust the Font Size and Colors

There's no email-address to send a bug report so I have to write it here in the reviews.

The new 1.0.0 Tab Tally version started to conflict with FlashStopper addon.
https://addons.mozilla.org/en-US/firefox/addon/flashstopper/

Steps to reproduce :
Create a new/fresh firefox profile.
Install the 2 addons.
Restasrt
Bookmark a page > The "OK" button looks dimmed.
It happens in many of the browser's other "special" windows and setting windows of many addons.

Workaround - Install TabTally previous version (0.1.1) and Restart browser.
Firefox 51
Win 7 x64

BTW - I reported the issue also here - http://forums.mozillazine.org/viewtopic.php?p=14730207#p14730207