This user script allows you to browse Wikipedia as it was at a given time in the past. It simplifies the investigation of the history of a discussion for example, as it allows you to move from a discussion to the corresponding articles or other pages, as they appeared at that day in the past.
Without this script, when you click on a link in an old page, you get the current version of the requested page, not its old one. To find the old one, you would need to search the corresponding pages manually in the history pages: what a waste of time!