ADDITIONAL SYSTEM INFORMATION :
- macOS (any version)
- Java 8 until current Java 11 and JavaFX 8 until current OpenJFX 11.0.1

A DESCRIPTION OF THE PROBLEM :
In the same spirit as https://bugs.openjdk.java.net/browse/JDK-8214069 and as suggested by Kevin Rushforth in https://github.com/javafxports/openjdk-jfx/issues/260#issuecomment-435082010 this issue is about not using the platform's default command to open documents and instead relying (here) on AWT's Desktop implementation for it.

I propose using a process (as is for Windows and Linux currently) and using "open <uri>" as the underlying command to let the OS pick the best-suited application according to OS/User settings, as is the recommended approach on Apple's operating system.