There are implementation differences, but it's not as if they were independent inventions. Mozilla's API is based directly on Chromium's. That itself is fine

There are implementation differences, but it's not as if they were independent inventions. Mozilla's API is based directly on Chromium's. That itself is fine (because Chromium is open-source), but I don't think a difference like callbacks vs promises makes it a unique product. If that's what you were implying, anyway.