Firefox 3 includes an interesting concept called places. The idea is that all history and bookmarks are stored in a SQLite database, and the browser exposes an API to interact with the data. You'll see it in action in the "Smart Bookmarks" button in the Bookmarks Toolbar -- these are dynamic queries against the database to find places you have visited the most, visited recently, etc.
I became interested in this because I started to write an extension for Firefox 2 to display all of the websites I work on that are in development -- the overhead was far too much for the return, so I stopped working on it.
Luckily, with Firefox 3, the places infrastructure allows me to do this very easily. For instance this bookmark will list out all of the items in your history, sorted recently visited first, that contain the text 'staging'. Quite handy.
I'm sure there is a better way to do this. I tried the uri parameter, but it kept crashing Firefox. In any case, it's a nice addition, and another testament to SQLite's applicability to many areas of web and application development.