Limit Tabs от RudyF

This add-on limits tabs by removing a tab -- newest (the one being added), least recently used, left-most or right-most -- when a new tab is added that takes the number of open tabs to more than the limit. Pinned tabs are ignored. The limit can be applied per window (default) or globally.

This was created to keep my autistic son sane. Without it, he would open a zillion tabs, then get frustrated when the system bogged down.

On installation, the tab limit will be set to the number of tabs in all windows.
Click the toolbar icon to toggle between enabled/disabled.
Use preferences to tweak the add-on to suit your needs.