Hi!
Thank you for trying to help. Well – I did add this rule but unfortunately without success. The menu still keeps jumping. There seems to be no easy way to solve tis problem. Think I have to live with it or may be I will find the time to develop a solution. Think I have to, because even knowing that there is a state my website looks shitty on every browser, drives me crazy. And I would feel the same, if nobody ever would size a window. of course I have to respect the decision of the developer to eliminate the useful function of defining a threshold for switching to mobile mode. I am sure there were reasons.
Thank you!
Niko