Websites loading from uberproxy-pen-redirect.corp.google.com

Questions

Which websites load from uberproxy-pen-redirect.corp.google.com?

The 424 sites listed on this page. A site is listed when its stored HTML has a script, iframe or stylesheet from the host, or one of its own scripts names the host in an absolute URL.

Is uberproxy-pen-redirect.corp.google.com a third party for every site listed?

Yes: a host under a site's own registrable domain is never recorded for that site, so every site here loads from uberproxy-pen-redirect.corp.google.com as a dependency outside its own domain.