If you are like me, you do not like the (Windows like) pop-ups on open taskbar applications.
In KDE 4 that used to be easy – System Settings -> Desktop Effects -> Taskbar Thumbnails
In KDE 5.8, it is a little different (as follows).
- Go to System Settings and Select Desktop Behavior
- Uncheck “Show Informational Tips”
That’s it – your thumbnail previews should be off.