Ah, ok - so, it looks like there have been recent changes to the location and function of httpd.js, and those changes are on trunk and have not propagated to release yet. And the documentation has been updated to the new way.

So what I'd suggest is to either start using Thunderbird Daily for testing and development (http://ftp.mozilla.org/pub/mozilla.org/thunderbird/nightly/latest-comm-central/), or build comm-central and use that...

OR, you can continue to develop on 17.0.6, but the documentation is going to fight you. If you go this route, your best bet is to search the comm-release mxr for examples on how to use httpd.js, like this: http://hg.mozilla.org/releases/comm-release/file/01292040cfad/mail/test/mozmill/shared-modules/test-cloudfile-yousendit-helpers.js

Let me know if you have any questions on this.