Max Tabs is a simple Firefox extension that auto close 1st tab when it reached max
https://addons.mozilla.org/en-US/firefox/addon/auto-close-tabs/
This is cloned from Cheeaun's https://github.com/cheeaun/max-tabs
https://addons.mozilla.org/en-US/firefox/addon/max-tabs/
bin\activate (Windows) or source bin/activate (Bash)
cfx run
cfx xpi