It does exactly what it says.

Clear Tabs
https://addons.mozilla.org/addon/clear-tabs/ and
Close Other Windows
https://addons.mozilla.org/addon/close-other-windows/ complement each other nicely.

Use case: https://github.com/MrAlex94/Waterfox/issues/551#issuecomment-399328071

A Clear Tabs option to not close pinned tabs would make a nice enhancement.

Excelente.