There is a Windows utility, QT Tabbar, that gives Windows Explorer a tabbed interface.

It mostly works, but I was seeing more Explorer flakiness than usual when I was using QT Tabbar, so I decided to remove it.

"Remove it."  Such a simple concept.  So easy in theory (run the uninstaller); so hard in practice (no uninstaller).

I had to resort to searching for files in C:\Windows (and below) containing "QT Tabbar" and searching the registry for "QT Tabbar" to remove it.