After one of the more recent updates, conkeror no longer liked my .conkerorrc file until I commented out
certain bits.  One of them was this:

/// /// Project Gutenbeg ///
/// define_webjump("books-gutenberg",
///     function (term) {
///         return load_spec(
///             { uri: "http://www.gutenberg.org/ebooks/search/",
///               post_data: make_post_data([['query', term]]) });
///     },
///     $alternative = "http://www.gutenberg.org/",
///     $argument = 'optional');

Is there something in that which no longer works?

remove the keyword $argument and you should be good.  webjumps were refactored recently, and this
keyword was found to be unnecessary.