Rated 5 out of 5 stars

@Han Solo, The same could be said about your browser history or most other functions in the browser. ;) URL Flipper doesn't store actual URLs (just hashes), so it's extremely difficult to reconstruct any private data from what it saves, and there's also a command to wipe everything. According to the bug tracker, integration with the leave-no-trace mode new to Firefox 3.5 is planned for a future release.

This review is for a previous version of the add-on (