How is this new? I can create a proxy server now, and I can share it with a friend and they can use my internet connection. They can do the same.

This is new because, It's likely easier to use, and it's all done in the browser.

The technology is certainly not new though...

Apache with mod_proxy, nginx, squid, ssh,

just to name a few of the many ways to do this...

Further to this, one doesn't need a browser plugin to do this, firefox for example already has configurable options to connect to proxy servers.