I'm not sure what the complaint is here. Isn't it something like 90% of the browser market is chromium-based, now that edge is on the bandwagon?

Supporting chrome/chromium doesn't seem like a bad place to start with a prototype with that kind of potential adoption.

You are right. In Firefox I get "StackBlitz v2 Beta currently works in Chrome and Chromium-based browsers. We’re hoping to add support for more browsers as they implement the necessary Web Platform features."