One could use a cloud service like Xmarks which already syncs bookmarks and browser passwords. Just because it's built into the browser doesn't mean that you can store the information in the cloud and sync it between browsers.
The difference is that you control the connection and your information directly. With OpenID or Facebook the connection is directly between those entities and site you are visiting. With a browser-based system, the connection is always between the site and you or the cloud and you.
The difference is that you control the connection and your information directly. With OpenID or Facebook the connection is directly between those entities and site you are visiting. With a browser-based system, the connection is always between the site and you or the cloud and you.