I recently had to develop a feature that would have been much easier to develop and debug had I been able to view the contents of Local Storage and Session Storage before loading the site.

A particular feature of a web application (shopping cart) had different behaviour depending if the page was loaded as "an initial pageview on revisit", e.g. the user coming from [search engine|other link|bookmark|url bar] or from normal site browsing. By storing data in both Local Storage and Session Storage, and comparing the two on page load, I could determine if the user, who had been to the site in the past, had just come back. This all had to be developed in the dark as the major browsers have no method of viewing Local Storage and Session Storage for websites not loaded.