Those are tabs just like the ones you see in your browser. They shouldn't be opening on their own while you scroll through the Folder Pane. You can close them all at once, except the one you want to keep open. For example, to close all the other tabs except Inbox, right-click on the Inbox tab (the first tab to the left, on your screenshot) then choose Close Other Tabs.

Thanks for your reply. Your solution does enable me to delete all the tabs en masse, however I'm looking for an answer to why this is happening and how I can prevent it. Thanks.

I have no idea why it happens on your end.

Is there anyone who can help???