Automating Firefox' address bar to explore forbidden web folders

"I've got a Firefox bookmarklet sitting on my toolbar to do just this, no add-on needed. Bookmarklets are just a single line of Javascript that you save as a bookmark, then when clicked they run on the current page.

If you look at the Miscellaneous Bookmarklets page you should see the Increment and Decrement bookmarklets that search the current URL for a number and either add one onto it, or take one off it. I just save those two to my toolbar and give them the labels ""+1"" and ""-1"" so they take up almost no space. Sounds like it's what you're after?"