In case anyone wants to delete the bibliographic data stored on Zotero (the Zotero info doesn’t help at all, as far as I could tell), here is what I did. I had over 5,000 items on Zotero which I wanted to delete. The reason is that I much prefer Bibdesk because it is flexible, fast, convenient, and works well with Textmate, XeLaTeX, and/or TeXShop for processing and pdf production. I couldn’t find a “data delete” button on the Zotero web page. So, I launched the Zotero extension (“add-on”) in Firefox, highlighted all the references in the library with shift-click, dragged them to the trash (or used Delete, I’m not sure anymore), then clicked on Trash and repeated the operation. “Sync” wiped the data on Zotero. Took a little while. Then I removed the Zotero folder left on my machine (Mac: /Users/username/Library/Application Support/Firefox/Profiles/random string/zotero) and whatever preference zotero files I had in /Library/Preferences. As for my Zotero account on the website, I removed it indirectly by deleting the email account associated with it. Cumbersome, but it worked.