We've been testing in Chrome on Windows, I just tested in DuckDuckGo on Windows and it worked for me. I unfortunately don't have a Mac to test on.
Looking into it a bit, the best guess I have is that this is a result of the shaky compatibility between Godot's web builds and macOS. In particular, there seems to be an ongoing issue with web builds that use multithreading (which our game does), but the best source I could find on this is this note from the docs. In retrospect, we probably don't need multithreading on this game lol, thanks for bringing this to our attention.