This is also true of web extensions. I suspect you've never developed one. You can't read another extension's data. It's also not true on desktop platforms. The user is still the security domain in desktop computing.

> As well as almost all regular software is backed by some large company with legal presence to hold responsible. The same can not [sic] be said for most extensions.

Is this true? All the browser extensions I use are published by a real legal entity that can be sued if they are negligent. What corner of the web are you on?