Solved with:
http://forum.mikrotik.com/t/dynamic-and-static-ip-mikrotik-routerboard-2011uias/153724/1
Dynamic and Static IP MikroTik RouterBOARD 2011UiAS
Looking back, I wonder:
I had/have connected the PC with EHTHER 2.
(learned: not EHTHER 1)
a) First, I had tried to ping with Firefox/Chrome
https://192.168.88.1
That did not work out.
b) Then I could connect with the winbox Windows App
c) After this, I could/can,
connect with Firefox/Chrome
https://192.168.88.1
(without winbox).