30 websites load from this host according to the stored source@if (Model.Total > HostModel.MaxSites) { ; the 200 highest-ranked are listed }. script, iframe and stylesheet are tags in the HTML; connect is an absolute URL inside one of the site's own scripts.
The 30 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 devcenter.heroku.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 devcenter.heroku.com as a dependency outside its own domain.