I have asked the developers the same question. As you know, you can use any browser to see a browser preview, but the 'external' preview is different. It has been IE all the time I've been using the Editor, only changing to newer versions as they appeared. The app and the IE 'engine' seem to be quite involved with each other, and as far as I've heard, it actually takes quite some brain cells to dissolve that relationship. That's all I know about it.
Ha en riktig god dag!
This site was made before we were able to create components through the app:
Component sharing for RFF, RBB, RSD and SD: https://eikweb.com/sharing/
My work in progress right now:
Components for the same as above + HTML Editor: https://mock-up.coffeecup.com