I just tested it again and it works for me as well! Maybe, the Firefox restart did help... Yes, I know about the WorldCat look-up, I did all the my tests withouth it. Actually, I would even vote for deleting (comment it out) the WorldCat look-up, when scraping the amazon webpage is working reasonably well (there is often a "mismatch" about edition, publication year, reprint, format, ...).