This is a slight change to the standard Zotero BibTeX exporter in order to work better with natbib, and fix the letter “ø”… I am using it with these patched versions of Writer2LaTeX and LyZ.

To use it:

• Download BibTeX-natbib.js and put it in your zotero/translators directory. On my system this is ~/.mozilla/firefox/bi3xapi2.default/zotero/translators (you can also choose to store your Zotero folder somewhere else, in the Zotero “advanced” settings)
• Restart Firefox. When you got to export, you’ll see it offered as a possibility. (Also, if you use the above LyZ-version, you can select BibTeX (natbib) from LyZ->Settings.)