> Every frame on a page was a separate, independent, coequal instance of the browser engine. This is almost never what you actually want.

Most frames are used for menu, navigation, frame for data, frame for additional information of data. And they are great for that. I don't think that frames are different instances of the browser engine(?) but that doesn't matter the slightest(?). They are fast and lightweight.

> The header/footer/sidebar frames are subordinate and should not navigate freely.

They have the ability to navigate freely but obviously they don't do that, they navigate different frames.