Packaging: To JAR or not to JAR

When I tried to package my extension, using a jar file did not work. But simply zipping everything in the extension folder (where install.rdf, chrome.manifest and content is) to a xpi file worked. Dunno what's up with that!

To clarify:
The packaging instructions here worked:
https://developer.mozilla.org/en/Buil...

The packaging instructions here did not:
https://developer.mozilla.org/en/Crea...