Hello Loy-ed, Clicking on the "X" at topr right corner of window closes the Firefox window not a particuar tab, the message you are getting is because you tried to close all the open tabs at once by closing the window .

If you want to close a particular tab then you can close it by clicking on to the "x" button present on that tab, it will only close the tab you selected.

Thank you.

And if a tab that you want to close doesn't have an X on the tab (not the active tab) you can middle-click the tab to close only that tab.