Update December 2016: This feature finally made it natively into Hacker News. This userscript is now obsolete.
This userscript adds a button to a Hacker News comment site to bring you back to the full thread.
It’s a head scratcher how this is not an existing feature on the site. The comment detail pages include no context as to which thread they belong to. Not even a title is included. When you land on a single comment from a Google Search, you’re pretty much stranded.
The only thing way out is to repeatedly click the little parent button until you reach the root of the thread. The first iteration of the script did exactly that: It repeatedly scraped the preceding comment’s page for the next URL. Later I learned about the Hacker News API but the API is limited so the process pretty much remained the same.
You can find the userscript here.