This is pretty cool, it definitely fits into my flow. One thing I noticed while browsing the code in page.js, I would probably change:

var getCommentUrl = function(anchor) { return $(anchor).closest('tr').next().find('a:nth-child(3)').prop('href'); };

to

var getCommentUrl = function(anchor) { return $(anchor).closest('tr').next().find('a[href^="item"]').prop('href'); };

Not that HN will ever change their html...