That was on my list of candidates as well! Those usually have a specific user agent making it clear what they are, they appear from a companies netblock (eg. Facebook, Microsoft) and cannot access authed pages (unless the key is in the url).

In this case these appeared to be all MitM'ed pages from a security device since the key wasn't in the url and it contained userids for a specific user.

In that case, the preview system would do (eg) GET https://example.com/private/page, but get a 401 Unauthorized response back, and have none of the page content or execute any of the scripts inlucded in that /private/page:

> * That somehow had the page content from a user

> * Would render and execute all scripts on that page as if it was that user