@ivo
Thank You
Works again with IE-11

... windy.com works fine with the actual version of Firefox.

Adding to my post the System in use:
WIN 7-SP1, IE 11.0.42 64bit

I have the same issue since about 15.06.2017 and did not find a solution with the given setup options. I also recognized that now one of the Settings I can not modify was set to "Low Bandwidth". I am using Windy(ty) since last year for spotting best places for modelplane soaring and judge myself as being a mature user.
Admins please comment / help.
Kind regards,
Volker