MaxTabsLimit-XT автор Cook I.T.

This extension allows you to limit the number of tabs you can open at the same time.
Additionally it displays how many tabs you have currently opened in multiple selectable formats.

• Global limit of tabs across all windows
• Quickly see how many tabs are open or left, with or without maximum tabs
• Open preferences and add-ons tab independent of tabs count
• Notification when max tabs are reached can be disabled or have a custom notification message
• Supports managed storage with locked settings for bigger rollouts (Example file)

This is a fork of MaxTabsLimit by gebirgsbaerbel, with big reworks to most parts except the tab counting/closing logic.