... for individual tweets.
To get a Tweet page with the old Twitter layout, an Internet
Explorer User-Agent (e.g. Mozilla/5.0 (Windows NT 6.1; WOW64;
Trident/7.0; rv:11.0) like Gecko) as well as a Referer header
pointing to the page itself is required. The "app_shell_visited"
cookie appears to be optional at the moment, but that is what
a regular web browser would send.