Well it was following the "IE standards". The difference is only rhetoric to avoid antitrust. Google dominates the standards. Edge is Chromium, Mozilla is maintained in survival mode by Google.
> Chrome does, pretty religiously
I wouldn't call it "religious" when Chrome follows stuff Google wants and Mozilla/Apple don't want.
> there are a number of open source browsers based on Chrome
Based on Chromium, you mean? That's still dominated by Google.