[petagonoral]

How many extensions need to send unique outbound data? Prior to publishing in store, browser maker can look at schema and query whether it makes sense in context of extension. If the submitted schema is not tight enough, it can be rejected until it's tighter.

[zulln]

A lot needs to modify the DOM, and that would make it possible to include a <img src=x width=0>. Preventing this seems _very_ complex.