As part of a project initialization routine, NetBeans creates a WebView and loads index.html from the attached Initializr_responsive.zip. It reportedly takes about 20s on one Windows computer, not reproducible on many others.

Attached javafx_thread.png is a profiler output taken on that computer. It shows the problem is likely in FXGraphicsManager.getSupportedMediaTypes(). Note that this method can cause initialization of JFX Media package.

There are two things to investigate:
1. Do we really need to know supported media types in this case? I can see no audio/video playing on the page.
2. Can we narrow down the problem to exclude either WebView or Media? E.g. by creating a Media-only test to reproduce the slowness.