Displays the number of open tabs in that window.

I was inspired by the following great add-ons, developed as an add-on for Firefox 57 or later.
Tab Counter
https://addons.mozilla.org/ja/firefox/addon/tab-counter/?src=dp-dl-othersby

Install

• License: Mozilla Public License 2.0
• Weekly downloads: 13
• Average daily users: 856
• Rating: 3.9583/5 of 24 ratings
• Created: 2017-09-29 13:42:30
• Last updated: 2017-09-29 14:10:14
• Homepage: https://github.com/sienori/Count-Tabs
• Support site and email
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• Orig: https://addons.mozilla.org/en-US/firefox/addon/count-tabs/
• API: Count-Tabs@sienori