because mv2 was more permissive with extensions, permit them to run native code and powerful processes. This is why bad extensions in mv2 are so dangerous.

With mv3 the idea is similar to what happened with android apps. Extensions are writed in a declarative way where they say what permissions they need and what they do, asking chromium to utilize the browser services they need.

At runtime chromium gives them the access they need in a restricted and compartimentalized way.

Like android apps cant access your media, just ask to android "hey I would access some media" talking to intermediary media-processes from the OS.

Mv3 ubo lite is more efficient, more maintainable and more secure, but lost a lot of advanced functions that required run native code in unrestricted processes.