How to allow the focus to follow the mouse in Windows 8.1

Some time ago, I wrote about a method how to get the focus to a background window, without raising it.

After some updates, I searched again for a method to allow the focus to follow the mouse and go to
this posting, which also references my previous source.

For some windows like Word, I have to move the mouse over the taskbar to switch
the focus.

With FullScreenMode on multiple screens, I have also some problems.
Also, the tip to decrease the value of the registry key ActiveWndTrkTimeout is very valuable.