As a long time user of the now seemingly-abandoned Location Navigator, URL Flipper has proven to be an excellent substitute. I especially like the ability to auto-seek up/down the number sequence until it finds one that works, rather than having to manually hunt for working URLs one number at a time.
However, there's one key feature that Location Navigator had, but URL Flipper doesn't: while browsing up or down, you could click a button to return to the original captured location. And this didn't just reload the starting location anew; it actually rolled back your browser history to the original page, just as if you had clicked the Back button multiple times to return to where you started. I found this really handy, because it let me "restore" my browser to the spot where I started flipping; when I finished browsing through a long sequence of numbers, I could just click "Return to Start" followed by the Back button, and pick up right where I left off before I started flipping.
It would be great if you could implement something similar for URL Flipper.