It's not open source. The Firefox Addon captured a visual snapshot and the entire page contents of every non-https page you visited, and stored it to an online database. The website allowed you to search your history, and results were based on number of visits to a page, length of time spent on page, number of times that page was selected as a search result, whether the page was actually bookmarked, etc. It was a very useful tool, but unfortunately the database grew large very fast. I tried to implement a subscription feature to offset server costs, but I had zero subscribers.

The code is all C#/MSSQL/JavaScript/XUL. If anyone's still interested gmail me at my username, and sorry for the off-topic posts!