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.