It can.

But it can't keep XUL compatibility and do major overhauls of the browser.

If XUL compatibility doesn't even get you a clear advantage in the add-ons area, should it block modernizing the browser?

Firefox can't be the browser that people use only because they're stuck on it because they have extensions that changes how the browser works. Think about that for a bit.

I know all about the issues with Firefox, the new WebExtensions and how the "old" XUL extensions which let you do "anything" are being phased out.

I just don't see how any of that is relevant to the original comment I replied to:

> But will Google allow this to happen, as it would strip them a huge selling point for Chrome?

In what way would standardizing WebExtensions, which are already supported by all modern browsers (sans Safari), strip Chrome of selling points?

Why should Google have to "allow" this?

Chrome currently has the largest amount of extensions, which is an advantage for that browser.

Standardized WebExtensions dilute that, because they allow easy ports to the other browsers.

I think the point is more, in what way does google have any power to stop other browsers from implementing this API?

They don't. Unless you want to claim API's are copyrightable, but there are some downsides to that :-)