The list of scripts in the script debugger UI can contain duplicates. This can happen for instance when multiple script tags or eval scripts are present in the same page. Either each script name should contain start line & line count numbers in the label, or each unique URL should appear once.
Went with the unique URL approach, as that is what the competition is doing. Fixed in https://hg.mozilla.org/users/dcamp_campd.org/remote-debug/rev/07a0ddb167d5