This plugin allows you to transform links to comments into a lightbox displaying comments without refreshing the page.
The lightbox works out of the box and require no configuration. It also takes care of matching the style of the currently active WordPress theme on your site.
Here is the requirement:
– Your theme must use the function comments_popup_link
– Your theme must use the original WordPress comments system (no Disqus or Facebook Comments)
It also provides a shortcode for creating buttons to open comments from anywhere on the site and that from any posts.