They're not testing the browser, they're testing the Web. Testing in the real world with real users is the only way to adequately probe the effects of potentially breaking changes like this.
This is not new either. Many such changes have been reverted after discovering that they broke more things than expected. One example is the Object.groupBy static method, which was initially Array.prototype.group.
> They're not testing the browser, they're testing the Web.
That sounds like a pretty lame excuse.
So if a self-driving car manufacturer does testing, they are not testing the car, they are testing the environment? Sounds like a pretty neat trick, maybe marketing should adopt this attitude.
This is not new either. Many such changes have been reverted after discovering that they broke more things than expected. One example is the Object.groupBy static method, which was initially Array.prototype.group.